SGI Glossary
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## SGI Glossary

4Dwm

  The name of the default Window Manager. See also window manager.

A bit

  The bit in Token Ring data frames that is set to zero when the frame is initially transmitted and set to one by the destination station when it has seen the frame. The original transmitting station uses the setting of this bit to decide whether or not to make additional transmissions to the destination station.

account

  See login account.

active monitor

  For 802.5 Token Ring, the one station (monitor) on the ring that is currently responsible for maintaining the ring's health. The duties of the active monitor include detecting and correcting error conditions, such as a lost token or a persistently circulating frame. The assignment of the active monitor is dynamically determined with the token claiming process each time the ring recovers from a fault.

active monitor present frame (AMP)

  A type of MAC frame (management frame) used to indicate the continuing presence of an active monitor on the ring. Only the active monitor issues these frames and it issues one about every 7 seconds. For the active monitor, this frame communicates the station's address to the next station (that is, the frame communicates the upstream neighbor address, UNA).

active setting (in IRIS Showcase)

  The setting used when you create a new object in IRIS Showcase. For example, when you select blue from the color palette and Helvetica from the text gizmo, you change the active setting. Graphics objects you draw are blue; text you type is Helvetica.

active state

  For Token Ring networks (including 802.5 Token Ring and FDDI), a ring condition in which data frames have been or are being transmitted onto the ring. This state is the opposite of the ring's idle state.

active video

  The portion of the video signal having the chrominance or luminance information; also, all video lines not in the vertical blanking signal that contain the chrominance or luminance information. See also chrominance, composite video, horizontal blanking, luminance, video waveform.

active window

  The only window that recognizes input (activity) from the keyboard and mouse; only one window is active at a time. Make a window active by placing the cursor within its boundaries.

adapter

  Also called a network adapter board or controller. A hardware device that is capable of communicating over a communications protocol medium; the adapter “speaks” the specific protocol (for example, 802.5 Token Ring, Ethernet, FDDI). Each station on a Token Ring must have an adapter through which it sends and receives data. The IRIS Token Ring board is an adapter. Two of the important functions performed by an adapter board are repeater and medium access control sublayer.

adapter cable

  The cable that connects an adapter to the network. The connection to the network is usually through a wall faceplate or directly to a trunk coupling unit (for example, a MAU or LAM). Two types of adapter cables are available: shielded twisted-pair cable ending in a DB-9 connector for the adapter, and unshielded twisted-pair cable ending in an RJ-45 connector for the adapter.

address space

  The set memory addresses that a process may legally access. The potential address space in IRIX is either 232 (IRIX 5.3) or 264 (IRIX 6.0); however, only addresses that have been mapped by the kernel are legally accessible.

administrator

  See network administrator, system administrator.

affinity scheduling

  The IRIX kernel attempts to run a process on the same CPU where it most recently ran, in the hope that some of the process's data remains in the cache of that CPU. The process is said to have “cache affinity” for that CPU. (“Affinity” means “a natural relationship or attraction.”)

aliasing

  A rendering technique that assigns to pixels the color of the primitive being rendered, regardless of whether that primitive covers all of the pixel's area or only a portion of the pixel's area. This results in jagged edges, or jaggies. In video systems, aliasing results when an image is sampled that contains frequency components above the Nyquist limit for the sampling rate. See also Nyquist limit.

align command (in IRIS Showcase)

  This IRIS Showcase command lets you line up objects. You can align objects to one another, to a grid, or sequentially.

alpha, alpha value

  The fourth color component of a pixel, specifying its opacity, translucency, or transparency. The alpha component is typically used to control color blending, and in video systems, is treated as a separate signal output. By convention, OpenGL alpha corresponds to the notion of opacity rather than transparency, meaning that an alpha value of 1.0 implies complete opacity, and an alpha value of 0.0 complete transparency.

alpha blending

  Overlaying one image on another so that some of the underlying image may or may not be visible. See also keying.

alpha plane

  A bank of memory that stores alpha values; the values are 8 bits per pixel.

alpha register

  A register that stores an alpha value.

alpha value

  See alpha.

American National Standards Institute (ANSI)

  The United States standardization body. ANSI produces documents that describe standards for information systems and input/output interfaces such as FDDI. ANSI is a member of the International Standards Organization (ISO).

AMP

  See active monitor present frame.

ANSI

  See American National Standards Institute.

antialiasing

  A rendering technique that assigns pixel colors based on the fraction of the pixel's area that's covered by the primitive being rendered. Antialiased rendering reduces or eliminates the jaggies that result from aliased rendering.

APL

  Average Picture Level, with respect to blanking, during active picture time, expressed as a percentage of the difference between the blanking and reference white levels. See also blanking level.

application-specific clipping

  Clipping of primitives against planes in eye coordinates; the planes are specified by the application using glClipPlane().

arena

  A segment of memory used as a pool for allocating objects of a particular type. Usually, the shared memory segment allocated by `usinit()`.

artifact

  In video systems, an unnatural or artificial effect that occurs when the system reproduces an image; examples are aliasing, pixellation, and contouring.

ASCII text

  ASCII text is characters onlynot the size, the font, the style, the color, or the format of the characters. When you save a file as ASCII text, you save only the characters.

aspect ratio

  The ratio of the width to the height of an image. For example, the standard aspect ratio for television is 4:3. Maintaining the original aspect ratio of an image prevents it from being distorted.

asynchronous I/O

  I/O performed in a separate process, so that the process requesting the I/O is not blocked waiting for the I/O to complete.

attaching device

  A generic term referring to any intelligent hardware and software system that can be inserted into a Token Ring (through an adapter and a trunk coupling unit). Some examples include printers, networked fax machines, mainframes, and stations (such as PCs and SGI workstations).

attenuation

  The weakening or diminishing of signal strength that can result in the loss of data.

autologin user

  The user who is automatically logged in to the system each time it is powered up.

average data rate

  The rate at which data arrives at a data collection system, averaged over a given period of time (seconds or minutes, depending on the application). The system must be able to write data at the average rate, provided that it has enough memory buffers to deal with bursts at the peak data rate. See also peak data rate.

back face

  See face.

back porch

  The portion of the horizontal pedestal that follows the horizontal synchronizing pulse. In a composite signal, the color burst is located on the back porch, but is absent on a YUV or GBR signal. See also blanking level, video waveform.

back up

  To copy a set of files and directories from your hard disk to a tape or other storage media.

backing store

  The disk location that contains the contents of a memory page. The contents of the page are retrieved from the backing store when the page is needed in memory. The backing store for executable code is the program or library file. The backing store for modifiable pages is the swap disk. The backing store for a memory-mapped file is the file itself.

backup tape

  A tape that contains a copy of a set of files and directories that are on your hard disk. A full backup tape contains a copy of all files and directories, including IRIX, that are on your hard disk.

bad blocks

  Occasionally, a part of a hard disk on a workstation may lose its ability to store information. When this happens, the piece of disk that has malfunctioned is known as a bad block. IRIX provides a facility to allow your workstation to skip over bad sections of disk and continue to use the rest of the disk.

bandwidth

  The range of frequencies that can be used for transmitting information on a channel, equal to the difference in hertz (Hz) between the highest and the lowest frequencies available on that channel. Bandwidth indicates the transmission capacity of a channel; the larger the bandwidth, the greater the amount of information that can pass through a circuit.

barrier

  A memory object that represents a point of rendezvous or synchronization between multiple processes. The processes come to the barrier asynchronously, and block there until all have arrived. Then all resume execution together.

baud rate

  The speed (calculated as bits per second) at which the computer sends information to a serial device, such as a modem or terminal. A part of line settings. See also line setting.

beacon frame (or beacon)

  For Token Ring networks (including 802.5 Token Ring and FDDI), a type of MAC frame (management frame) used to indicate a break in the ring. Only standby monitors issue these frames. The presence of this type of frame on a ring indicates that a station thinks it has detected a break in the ring and that the beaconing procedure is in progress.

beacon process, or beaconing

  For Token Ring networks (including 802.5 Token Ring and FDDI), a ring recovery process that starts when a station fails to see a token after a set period of time while token claiming. During the beaconing process, one or more stations transmit beacon frames until the ring is again intact (that is, the break in the ring is fixed). All stations refrain from transmitting data during beaconing. When a beaconing station sees another station's beacon frame, it stops beaconing. When a beaconing station sees its own beacon frame, it starts token claiming.

Betacam

  A component videotape format developed by Sony® that uses a Y/R-Y/B-Y video signal and 1/2-inch tape.

Betacam format

  Advanced form (Superior Performance) of Betacam using special metal tape and offering longer recording time (90 minutes instead of 30 minutes) and superior performance.

bit

  Binary digit. A state variable having only two possible values: 0 or 1. Binary numbers are constructions of one or more bits.

bitmap (in OpenGL)

  A rectangular array of bits. Also, the primitive rendered by the glBitmap() command, which uses its bitmap parameter as a mask.

bit map (in video systems)

  A region of memory that contains the pixels representing an image. The pixels are arranged in the sequence in which they are normally scanned to display the image.

bitplane

  A rectangular array of bits mapped one-to-one with pixels. The framebuffer is a stack of bitplanes.

black burst

  Active video signal that has only black in it. The black portion of the video signal, containing color burst. See also color burst.

black level

  In the active video portion of the video waveform, the voltage level that defines black. See also horizontal blanking, video waveform.

blanking level

  The signal level at the beginning and end of the horizontal and vertical blanking intervals, typically representing zero output (0 IRE). See also video waveform, IRE units.

blending

  Combining two color components into one, usually as a linear interpolation between the two components. The alpha value helps determine how the components are combined. See also alpha; for video-related terms, see also key, frame.

block

  A group of digits, characters, or words that are held in one section of an input/output medium and handled as a unit. Within the IRIX filesystem, a block of disk space consists of 512 bytes.

boot block

  The boot block is the first block of each filesystem. A filesystem block is 512 bytes. The boot block is read for instructions when the system is booted. These instructions are for the hardware and are not used by the operating system.

BOOTP

  The networking protocol that provides the service for booting a computer over a network connection. BOOTP is essential to diskless workstation operation.

borderless window

  A window with no title bar or borders.

break in the ring

  For Token Ring networks (including 802.5 Token Ring and FDDI), a ring error condition where the signal cannot complete the loop from a repeater's output port around the ring to the same repeater's input port. Whenever a station fails to see the token or an active monitor present frame for a defined period of time, a break in the ring is assumed and beaconing starts.

breezeway

  In the horizontal blanking part of the video signal, the portion between the end of the horizontal sync pulse and the beginning of the color burst. See also horizontal blanking, video waveform.

broad pulses

  Vertical synchronizing pulses in the center of the vertical interval. These pulses are long enough to be distinguished from other pulses in the signal; they are the part of the signal actually detected by vertical sync separators.

Bruch blanking

  In PAL signals, a four-field burst blanking sequence that assures that burst phase is the same at the end of each vertical interval.

buffer

  A group of bitplanes that store a single component (such as depth or green) or a single index (such as the color index or the stencil index). Sometimes the red, green, blue, and alpha buffers together are referred to as the color buffer, rather than the color buffers.

burst, burst flag

  See color burst.

burst lock

  The ability of the output subcarrier to be locked to input subcarrier, or of output to be genlocked to an input burst.

burst phase

  In the RS-170A standard, burst phase is at field 1, line 10; in the European PAL standards, it is at field 1, line 1. Both define a continuous burst waveform to be in phase with the leading edge of sync at these points in the video timing. See also vertical blanking interval, video waveform.

button

  On a mouse, a button is a switch you press with a finger. In a window on your screen, a button is a labeled rectangle you click using the cursor and mouse.

B-Y (B minus Y) signal

  One of the color difference signals used on the NTSC and PAL systems, obtained by subtracting luminance (Y) from the blue camera signal (B). This signal drives the horizontal axis of a vectorscope. Color mixture is close to blue; phase is 180 degrees opposite of color sync burst; bandwidth is 0.0 to 0.5 MHz. See also luminance, R-Y signal, Y signal, Y/R-Y/B-Y.

bypass

  The ability of an FDDI node to isolate itself optically from the ring while maintaining the integrity of the rest of the ring.

bypass state

  For Token Ring networks (including 802.5 Token Ring and FDDI), a state in which a station is not inserted onto the ring. The station is not listening, repeating, or transmitting when in the bypass state. If a station is attached to a trunk coupling unit (TCU)or optical bypass switch (OBS), the TCU/OBX may bypass the station if it determines that the station is dysfunctional. This action should cause the station to transition into its bypass state.

C bit

  The bit in Token Ring data frames that is set to zero when the frame is initially transmitted and set to one by the destination station when it has copied the frame. The original transmitting station uses the setting of this bit to decide whether or not to retransmit the data within that frame.

C format

  Type C, or 1-inch reel-to-reel videotape machine; an analog composite recording format still used in some broadcast and postproduction applications.

C signal

  Chrominance; the color portion of the signal. For example, the Y/C video format used for S-VHS has separate Y (luminance) and C (chrominance) signals. See also chrominance.

canonical order

  In the computer world, the term bit order is analogous to the order for reading a flow of letters in text. Canonical order is somewhat like reading across the page from left to right (as English speakers normally do) but reading each word from right to left. So, the characters`TIME WAR` would be read as “emit raw.” To compare this to a different ordering, see FDDI order.

  In more technical terms, canonical order is a method for representing the 48-bit (6-byte) sequences used for addresses in FDDI. This method considers the first bit transmitted within each byte to be the least significant bit. For example, the sequence <1 followed by 0, 0, 0> is represented as 1 in decimal (not as 8). This is the ordering traditionally used for Ethernet addresses and is bit-swapped within each byte with respect to FDDI ordering. For the bytes themselves, the first transmitted byte is considered to be the most significant byte.

  The SMT commands represent each byte of a canonically ordered FDDI address as a hexadecimal value (two hexadecimal characters) separated by a colon (:), for example, 08:00:69:a4:0c:d0. See also FDDI order.

CAU

  See controlled access unit.

CAV

  Component Analog Video; a generic term for all analog component video formats, which keep luminance and chrominance information separate. D1 is a digital version of this signal. See also component video.

CCIR 601

  The digital interface standard developed by the CCIR (Comité Consultatif International de Radiodiffusion, or International Radio Consultative Committee) based on component color encoding, in which the luminance and chrominance (color difference) sampling frequencies are related in the ratio 4:2:2: four samples of luminance (spread across four pixels), two samples of CR color difference, and two samples of CB color difference. The standard, also referred to as 4:2:2, sets parameters for both 525-line and 625-line systems.

CD-ROM disc (CD)

  A flat metallic disc that contains information you can view and copy onto your own hard disk; you cannot change or add to its information. CD-ROM is short for compact-disc: read-only memory.

CDDI

  See copper distributed data interface.

CEM

  See configuration element management.

CFM

  See configuration management.

chassis

  The structural metal framework that contains the CPU and other working parts.

choose

  To press the left mouse button to bring up a pop-up menu, move the cursor to highlight the command you want, then release the button.

chroma

  See chrominance.

chroma keying

  Overlaying one video source on another by choosing a key color. For example, if chroma keying is on blue, video source A might show through video source B everywhere the color blue appears in video source B. A common example is the TV weather reporter standing in front of the satellite weather map. The weather reporter, wearing any color but blue, stands in front of a blue background; keying on blue shows the satellite picture everywhere blue appears. Because there is no blue on the weatherperson, he or she appears to be standing in front of the weather map.

chroma signal

  A 3.58 MHz (NTSC) or 4.43 MHz (PAL) subcarrier signal for color in television. SECAM uses two frequency-modulated color subcarriers transmitted on alternate horizontal lines; SCR is 4.406 MHz and SCB is 4.250 MHz.

chrominance

  In an image reproduction system, a separate signal that contains the color information. Black, white, and all shades of gray have no chrominance and contain only the luminance (brightness) portion of the signal. However, all colors have both chrominance and luminance.

  Chrominance is derived from the I and Q signals in the NTSC television system and the U and V signals in the PAL television system. See also luminance.

chrominance signal

  Also called the chroma, or C, signal. The high-frequency portion of the video signal (3.58 MHz for NTSC, 4.43 MHz for PAL) color subcarrier with quadrature modulation by I (R-Y) and Q (B-Y) color video signals. The amplitude of the C signal is saturation; the phase angle is hue. See also color subcarrier, hue, saturation.

cladding

  The low refractive index material that surrounds the core of an optical cable.

claim

  As a verb, see capture. As a noun, see claim token frame.

claim process

  A process in which stations bid for the right to initialize the Token Ring.

claim token frame (or claim)

  A type of MAC frame (management frame) used to manage the token claiming process. Any standby monitor may use this frame.

class

  A group of all printers of a given type. You define the types of printers. For example, all printers in a given room might be grouped as a class, or all laser printers might be a class.

click

  To hold the mouse still, then press and immediately release a mouse button.

client (in OpenGL)

  The computer from which OpenGL commands are issued. The computer that issues OpenGL commands can be connected via a network to another computer that executes the commands, or commands can be issued and executed on the same computer. See also server.

client (in Video Library)

  An application that has connected to the video daemon to perform video requests.

client memory

  The main memory (where program variables are stored) of the client computer.

clip coordinates

  The coordinate system that follows transformation by the projection matrix and that precedes perspective division. View-volume clipping is done in clip coordinates, but application-specific clipping is not.

clipping

  Elimination of the portion of a geometric primitive that's outside the half-space defined by a clipping plane. Points are simply rejected if they are outside. The portion of a line or of a polygon that's outside the half-space is eliminated, and additional vertices are generated as necessary to complete the primitive within the clipping half-space. Geometric primitives and the current raster position (when specified) are always clipped against the six half-spaces defined by the left, right, bottom, top, near, and far planes of the view volume. Applications can specify optional application-specific clipping planes to be applied in eye coordinates.

CMT

  See connection management.

color bars

  A test pattern used by video engineers to determine the quality of a video signal, developed by the Society of Television and Motion Picture Engineers (SMPTE). The test pattern consists of equal-width bars representing black, white, red, green, blue, and combinations of two of the three RGB values: yellow, cyan, and magenta. These colors are usually shown at 75% of their pure values.

color burst

  The segment of the horizontal blanking portion of the video signal that is used as a reference for decoding color information in the active video part of the signal. The color burst is required for synchronizing the phase of 3.58 MHz oscillator in the television receiver for correct hues in the chrominance signal.

  In composite video, the image color is determined by the phase relationship of the color subcarrier to the color burst. The color burst sync is 8 to 11 cycles of 3.58 MHz color subcarrier transmitted on the back porch of every horizontal pulse. The hue of the color sync phase is yellow-green.

  Also called burst and burst flag. See also color subcarrier, video waveform.

color difference signals

  Signals used by color television systems to convey color information so that the signals go to zero when the picture contains no color; for example, unmodulated R-Y and B-Y, I and Q, U, and V.

color-frame sequence

  In NTSC and S-Video, a two-frame sequence that must elapse before the same relationship between line pairs of video and frame sync repeats itself. In PAL, the color-frame sequence consists of four frames.

color index

  A single value that represents a color by name, rather than by value. OpenGL color indices are treated as continuous values (for example, floating-point numbers) while operations such as interpolation and dithering are performed on them. Color indices stored in the framebuffer are always integer values, however. Floating-point indices are converted to integers by rounding to the nearest integer value.

color-index mode

  An OpenGL context is in color index mode if its color buffers store color indices, rather than red, green, blue, and alpha color components.

color map

  A table of index-to-RGB mappings that's accessed by the display hardware. Each color index is read from the color buffer, converted to an RGB triple by lookup in the color map, and sent to the monitor.

color palette (in IRIS Showcase)

  The collection of colors you can use in IRIS Showcase.

color space

  A space defined by three color components, such as R, G, and B.

color subcarrier

  A portion of the active portion of a composite video signal that carries color information, referenced to the color burst. The color subcarrier's amplitude determines saturation; its phase angle determines hue. Hue and saturation are derived with respect to the color burst. The color subcarrier's frequency is defined as 3.58 MHz in NTSC and 4.43 MHz in PAL. See also color burst.

comb filtering

  Process that improves the accuracy of extracting color and brightness portions of the signal from a composite video source.

command line option

  Options that let you specify how you want to run an IRIX command. See the man page for a command for a list of the available command line options.

complementary color

  Opposite hue and phase angle from a primary color. Cyan, magenta, and yellow are complementary colors for red, green, and blue, respectively.

component

  A single, continuous (for example, floating-point) value that represents an intensity or quantity. Usually, a component value of zero represents the minimum value or intensity, and a component value of one represents the maximum value or intensity, though other normalizations are sometimes used. Because component values are interpreted in a normalized range, they are specified independent of actual resolution. For example, the RGB triple (1, 1, 1) is white, regardless of whether the color buffers store 4, 8, or 12 bits each.

  Out-of-range components are typically clamped to the normalized range, not truncated or otherwise interpreted. For example, the RGB triple (1.4, 1.5, 0.9) is clamped to (1.0, 1.0, 0.9) before it's used to update the color buffer. Red, green, blue, alpha, and depth are always treated as components, never as indices.

component video

  A color encoding method for the three color signals—R, G, and B; Y, I, and Q; or Y, U, and V—that make up a color image. See also RGB, YIQ, YUV.

component video signals

  A video signal in which luminance and chrominance are sent as separate components to yield a signal with a higher color bandwidth than that of composite video. Examples of component video signals are:

  - RGB (basic signals generated from a camera)

  - YIQ (used by the NTSC broadcasting standard)

  - Y/R-Y/B-Y (used by Betacam and M-II recording formats and SECAM broadcasting standard)

  - YUV (subset of Y/R-Y/B-Y used by the PAL broadcasting standard)

  Separating these components yields a signal with a higher color bandwidth than that of composite video.

  See also chrominance, composite video, luminance, RGB, YIQ, YUV.

composite video

  A color encoding method or a video signal that contains all of the color, brightness, and synchronizing information in one signal. The chief composite television standard signals are NTSC, PAL, and SECAM. See also NTSC, PAL, SECAM.

computer

  An electronic device that performs arithmetic calculations and processes and stores data. It may be a standalone unit or connected to other units.

CON

  See concentrator.

concave

  Nonconvex. See convex.

concentrator (CON)

  For Token Ring networks (including 802.5 Token Ring and FDDI), a hardware device that allows multiple stations to attach to it so that they can participate in the ring without being directly attached to the trunk ring. Concentrators enhance ring robustness because they include the functionality of a trunk coupling unit or optical bypass switch for each of their attached stations.

  In FDDI environments, the concentrator provides M ports, to which single-attachment S ports of other FDDI stations (including other concentrators) are attached in a tree topology. In 802.5 Token Ring environments, multistation access units and lobe attachment modules are examples of concentrators.

confidence test

  A test that you run to make sure a particular device (such as the keyboard, mouse, or a drive) is set up and working properly.

configuration element management (CEM)

  The portion of connection management (CMT) for Token Ring nodes that manages the configuration of a port and, if present, its MAC. There is one instance of this functionality for each port on a station or concentrator.

configuration file

  A system file you can change to customize the way your system behaves. Such files are also called customization files.

configuration management (CFM)

  The portion of the station management for Token Ring nodes that manages the configuration of the station's MAC and PHY entities.

configuration report server

  Also called network manager. For 802.5 Token Ring, an application-level software module, residing within one station on the ring, for managing ring parameters and statistics. The presence of a configuration report server on a ring is optional. (SGI does not currently provide this software module.)

connection management (CMT)

  The portion of the FDDI SMT that manages the operation of the physical layer. CMT functionality is divided into three areas: physical connection management (PCM), configuration element management (CEM), and entity coordination management (ECM). CMT monitors the primary and secondary rings, isolates and wraps around noisy or quiet links, prevents stations from entering the ring in an illegal topology, and verifies when a faulty link has been fixed and unwraps the ring.

connector

  Hardware at the end of a cable that lets you fasten the cable to an outlet, port, or another connector.

connector plug

  A device used to terminate an optical signal transmission cable. The male half of an optical signal transmission cable connection. Connector plugs connect to receptacles. See also connector receptacle, media interface connector, straight tip connector.

connector receptacle

  A device used to terminate an optical signal transmission cable. The female half of an optical signal transmissions cable connection. Receptacles connect to plugs. See also connector plug, media interface connector, straight tip connector.

console

  The window that appears as a stowed icon each time you log in; IRIX reports all status and error messages to this window.

context

  A complete set of OpenGL state variables. Note that framebuffer contents are not part of OpenGL state, but that the configuration of the framebuffer is.

context switch time

  The time required for IRIX to set aside the context, or execution state, of one process and to enter the context of another; for example, the time to leave a process and enter a device driver, or to leave a device driver and resume execution of an interrupted user process.

controlled access unit (CAU)

  For 802.5 Token Ring, an intelligent hardware device that provides diagnostic support for the ring. A CAU is always associated with a lobe attachment module.

convex

  A polygon is convex if no straight line in the plane of the polygon intersects the polygon more than twice.

convex hull

  The smallest convex region enclosing a specified group of points. In two dimensions, the convex hull is found conceptually by stretching a rubber band around the points so that all of the points lie within the band.

coordinate system

  In n-dimensional space, a set of n linearly independent vectors anchored to a point (called the origin). A group of coordinates specifies a point in space (or a vector from the origin) by indicating how far to travel along each vector to reach the point (or tip of the vector).

copper distributed data interface (CDDI)

  An FDDI-like protocol that uses copper cabling (either shielded or unshielded twisted-pair) instead of fiber optic cabling for attaching nodes to concentrators.

core (optical transmission media)

  The central transmission area of a fiber. The core always has a refractive index higher than that of the cladding. The core acts as a wave guide and confines the signal.

counter-rotating

  An arrangement in which the light signal within each loop of a dual ring (for example, an FDDI ring) travels in opposite directions.

CPU-intensive

  A process or program that requires a great deal of calculation or operation on the part of the CPU is considered CPU-intensive. For example, a program that calculates the value of pi to one million places is considered CPU-intensive. The speed of the CPU bus and the clock rate of the CPU itself are the limiting factors on the speed of a CPU-intensive program.

cross-chrominance, cross-luminance

  Also known as cross-color, hanging dots, dot crawl; moving colors on stationary objects. This undesirable artifact is caused by high bandwidth luminance information misinterpreted as color information. Hanging dots are a by-product of the comb filters (used to help separate the color and brightness information) found in most modern television receivers. This artifact can be reduced or eliminated by using S-Video or a component video format.

cross-fade

  A type of transition in which one video clip is faded down while another is faded up.

culling

  The process of eliminating a front face or back face of a polygon so that it is not drawn.

current matrix

  A matrix that transforms coordinates in one coordinate system to coordinates of another system. There are three current matrices in OpenGL: the modelview matrix transforms object coordinates (coordinates specified by the programmer) to eye coordinates; the perspective matrix transforms eye coordinates to clip coordinates; the texture matrix transforms specified or generated texture coordinates as described by the matrix. Each current matrix is the top element on a stack of matrices. Each of the three stacks can be manipulated with OpenGL matrix-manipulation commands.

current raster position

  A window coordinate position that specifies the placement of an image primitive when it's rasterized. The current raster position, and other current raster parameters, are updated when glRasterPos() is called.

current working directory

  The directory within the filesystem in which you are currently located when you are working in a shell window.

cursor

  The small red arrow or other shape on the screen that follows the movements of the mouse. It may change shape depending on its location on the screen.

cut

  To remove objects or text from the page and place them in a cut buffer.

D1

  Digital recording technique for component video; also known as CCIR 601, 4:2:2. D1 is the best choice for high-end production work, where many generations of video are needed. D1 can be an 8-bit or 10-bit signal. See also CCIR 601.

D2

  Digital recording technique for composite video. As with analog composite, the luminance and chrominance information is sent as one signal. A D2 VTR offers higher resolution and can make multiple generation copies without noticeable quality loss, because it samples an analog composite video signal at four times the subcarrier (using linear quantization), representing the samples as 8-bit digital words. D2 is not compatible with D1.

D3, DX

  Developed by Panasonic, a 1/2-inch tape version of D2. More often called DX.

DA

  See destination address.

daemons

  Programs that are run automatically by the system for a specific purpose. For example, `timed`, the time daemon checks the current time on the system against a master clock on another system.

DAS

  See dual-attachment station.

DAT (Digital Audio Tape)

  A magnetic tape from which you can read and to which you can copy audio and digital information. The SGI DAT drive can be used with both audio and digital media.

Data Carrier Detect (DCD)

  A signal that a modem carrier tone has been detected. The DCD signal is sent on pin 8 of an RS-232 cable.

Data Communications Equipment (DCE)

  A type of serial interface. DCE devices transmit data on pin 3 and receive on pin 2. See null modem.

data frame

  Token Ring frames that contain user data in the “Information” segment

data link layer

  Network layer 2 for both the Open Systems Interconnect and the Systems Network Architecture environments. The data link layer is responsible for data transfer across a single physical connection. For Token Ring, the services of this layer are divided into two sublayers: medium access control and logical link control.

data link provider interface (DLPI)

  In an SNA environment, the interface (language for talking) to the SNA data link layer.

Data Terminal Equipment (DTE)

  A type of serial interface. DTE devices transmit data on pin 2 and receive on pin 3. The serial ports for workstations and servers are configured as DTE. Most terminals are also configured as DTE. See null modem.

Data Terminal Ready (DTR)

  A signal that the terminal is ready to give and receive information. This signal is sent on pin 9 of a 9-pin cable and pin 20 on an RS-232 cable.

deadline scheduling

  A process scheduling discipline supported by IRIX version 5.3. A process may require that it receive a specified amount of execution time over a specified interval, for instance 70 ms in every 100 ms. IRIX adjusts the process's priority up and down as required to ensure that it gets the required execution time.

deadlock

  A situation in which two (or more) processes are blocked because each is waiting for a resource held by the other.

decibel (dB)

  A standard unit that uses a logarithmic scale for expressing transmission gain or loss and relative power levels.

decoder

  Hardware or software that converts, or decodes, a composite video signal into the various components of the signal. For example, to grab a frame of composite video from a VHS tape deck and store it as an RGB file, it must be decoded first. Several SGI video options have on-board decoders.

default printer

  The printer to which the system directs a print request if you do not specify a printer when you make the request. You set the default printer using the Print Manager.

defaults

  A set of behaviors that SGI specifies on every system. You can later change these specifications, which range from how your screen looks to what type of drive you want to use to install new software. For example, when you run IRIS Showcase, the Master gizmo opens by default. You can change the default settings using the Preferences gizmo.

delete (in IRIS Showcase)

  To permanently remove an object from an IRIS Showcase page. Once you've removed them, you cannot retrieve objects by choosing Paste.

depth

  Generally refers to the z window coordinate.

depth-cueing

  A rendering technique that assigns color based on distance from the viewpoint.

destination

  The printer where a file is printed.

destination address (DA)

  The address of the entity that is the intended recipient of the data. The format for the address is different for each protocol. A single node has different addresses for its different layers (such as data link layer addresses versus network layer ones). Examples are: FDDI and 802.5 use 16-bit or 48-bit addresses; Ethernet uses 48-bit addresses; HIPPI uses 24-bit addresses; IP uses 32-bit addresses.

device driver

  Code that operates a specific hardware device and handles interrupts from that device.

device numbers

  Each I/O device is represented by a name in the `/dev` filesystem hierarchy. When these “device special files” are created (see the makedev(1) reference page), they are given major and minor device numbers. The major number is the index of a device driver in the kernel. The minor number is specific to the device; it encodes information such as its unit number, density, VME bus address space, or similar hardware-dependent information.

device service time

  The amount of time spent executing the code of a device driver in servicing one interrupt. One of the three main components of interrupt response time. See also interrupt response time

device special file

  The symbolic name of a device that appears as a filename in the `/dev` directory hierarchy. The file entry contains the device numbers that associate the name with a device driver.

diagnostics

  A series of tests that check the hardware components of your system.

diagnostics terminal

  The ASCII terminal connected to the port labeled 1 on the I/O panel of a server. Error messages and diagnostics information produced by the power-on diagnostics appear on the screen of this terminal.

dialup password

  An extra password required by a workstation from users who are accessing the system through a modem connected to an external phone line. This password is required before the login process can begin. It provides an added level of security against intruders.

direct memory access (DMA)

  Independent hardware that transfers data between memory and an I/O device without direct program control. The Challenge/Silicon Graphics Onyx systems have a DMA engine for the VME bus.

directory

  A special file in the filesystem in which you can store other directories and files.

disk-intensive

  A program or process that requires large amounts of data to be read from or written to the hard disk is considered disk-intensive. For example, a program that saves its entire working buffer to the disk once per second is considered disk-intensive. The limiting factor on the speed of disk-intensive programs is the time required for the disk access.

disk label

  A section of the hard disk that stores information about the contents of the rest of the disk.

disk resource

  Any disk (hard, CD-ROM, or floppy) can access either because it is physically attached to your workstation with a cable, or it is available over the network using NFS. See also NFS.

disk use

  The percentage of space on your disk that contains information.

display list

  A named list of OpenGL commands. Display lists are always stored on the server, so display lists can be used to reduce network traffic in client-server environments. The contents of a display list may be preprocessed, and might therefore execute more efficiently than the same set of OpenGL commands executed in immediate mode. Such preprocessing is especially important for computing intensive commands such as glTexImage().

distributed network

  A computer network that has no automated central control of services or information. Each system's administrator must work with the network administrator to keep each system's network information up to date. See also centralized network.

dithering

  A technique for increasing the perceived range of colors in an image at the cost of spatial resolution. Adjacent pixels are assigned differing color values; when viewed from a distance, these colors seem to blend into a single intermediate color. The technique is similar to the halftoning used in black-and-white publications to achieve shades of gray.

DLPI

  See data link provider interface.

domain

  A group of hosts on a network whose hostnames have the same suffix. See also NIS domain.

domain name

  The common suffix found in all hostnames that are in the same domain on a network. See also NIS domain.

dotted decimal notation

  A way of representing a 32-bit (4-byte) Internet address in ASCII. Each byte of the address is represented as a decimal number (ranging in value from 0 to 255). Bytes are separated by a dot (.). For example, 126.52.4.89. See also Internet address.

double-buffering

  OpenGL contexts with both front and back color buffers are double-buffered. Smooth animation is accomplished by rendering into only the back buffer (which is not displayed), then causing the front and back buffers to be swapped.

double-click

  To hold the mouse still, then press and release it twice, very rapidly. When you double-click an icon, it opens into a window; when you double-click the Window menu button (in the upper left corner of a window), the window closes.

downstream

  The direction of a signal's flow.

drag

  To press and hold down a mouse button, then move the mouse. This drags the cursor to move icons or to highlight menu items.

drain

  In the context of the Video Library, a target or consumer of video signals.

drawing area (in IRIS Showcase)

  The area in which you draw or place objects.

drive

  A hardware device that lets you access information on various forms of media, such as hard, floppy, and CD-ROM disks, and magnetic tapes.

drive address

  See SCSI address.

dual ring

  An FDDI ring configuration with two separate loops (rings) of fiber optic cable. It is common for one loop to be the main (primary) ring and the other to be used as a backup. In this configuration, the ring can wrap to reestablish communication when there are problems with the primary ring. It is also possible to configure both rings as main (data carrying) networks.

dual-attachment station (DAS)

  An FDDI station that offers two connections (attachments) to the FDDI ring. The two connections can connect to the primary and secondary rings, or the two can be attached to a concentrator for a dual-homed configuration.

dual-fiber cable

  A type of optical fiber cable that has two single-fiber cables enclosed in a jacket of extruded PVC, with a ripcord for pulling back the jacket to access the fibers.

dual-homed

  An FDDI DAS configuration in which both ports are connected as S-type ports to a concentrator. Port A is connected to one M-type port and B is connected to a different M-type port on the same or a different concentrator. This configuration provides a backup interface if one port should fail. Synonym: tree connection with redundancy.

dumpster

  The icon onto which you drag files when you want to delete them. The dumpster icon appears in your home directory and the WorkSpace window.

duplicate address

  An error condition in which two stations on a network use the same physical address (MAC address).

duplicate address test frame (DAT)

  For 802.5 Token Ring, a type of MAC frame (management frame) used by a station during initialization to verify that its physical address (MAC address) is unique on the ring. All stations use this type of frame when they insert themselves onto the ring.

early token release

  An optional set of rules for governing Token Ring data transmission, frame stripping, and token release. This enhancement is available only for 16-megabit-per-second Token Rings. The rules allow a transmitting station to regenerate (release) the token before stripping all of its data frames and allow the next station to start transmitting. Early token release makes it possible for more than one data frame to be on the ring at a time, thus increasing the ring's efficiency (or use of bandwidth).

ECM

  See entity coordination management.

edit (in IRIS Showcase)

  In IRIS Showcase, you edit an object when you want to alter its individual elements—letters and words in a Text object, and points in a Graphics object.

editing

  The process in which data is examined, created, and modified. In video, the part of the postproduction process in which the finished videotape is derived from raw video footage. Animation is a subset of editing.

element

  A single component or index.

encoder

  Device that combines the R, G, and B primary color video signals into hue and saturation for the C portion of a composite signal. Several SGI video options have on-board encoders.

entity coordination management (ECM)

  The portion of CMT that manages the media interface to the FDDI network, which includes coordinating the activity of all of the PHYs associated with that physical attachment, and controlling the optional optical bypass function within the station. There is only one instance of this functionality on a station or concentrator.

environment

  When you set all the preferences for the shell, commonly used applications, the window manager, and the system in general, together those settings are called the environment. Usually, when speaking of the environment, only the shell settings are included.

EPS (Encapsulated PostScript)

  You can save your IRIS Showcase files as EPS and import them into other programs that accept EPS files.

equalizing pulse

  Pulse of one half the width of the horizontal sync pulse, transmitted at twice the rate of the horizontal sync pulse, during the portions of the vertical blanking interval immediately before and after the vertical sync pulse. The equalizing pulse makes the vertical deflection start at the same time in each interval, and keeps the horizontal sweep circuits in step during the portions of the vertical blanking interval immediately before and after the vertical sync pulse.

Ethernet order

  See canonical order.

evaluation (in OpenGL)

  The OpenGL process of generating object-coordinate vertices and parameters from previously specified Bézier equations.

event

  Exceptional or noteworthy condition produced during video processing, such as loss of sync, dropping of frames or fields, and synchronization with other applications.

exclusive use

  A term applied to use of the video data stream and controls on a pathway. A pathway in exclusive-use mode is available for writing of controls only to the client that requested the exclusive use, yet any application may read the controls on that pathway.

execute (in OpenGL)

  An OpenGL command is executed when it's called in immediate mode or when the display list that it's a part of is called.

export

  To use NFS software to make all or part of your filesystem available to other users and systems on the network.

external device

  A piece of hardware attached to the workstation with a cable.

eye coordinates

  The coordinate system that follows transformation by the modelview matrix and that precedes transformation by the projection matrix. Lighting and application-specific clipping are done in eye coordinates.

face (in OpenGL)

  One side of a polygon. Each polygon has two faces: a front face and a back face. Only one face or the other is ever visible in the window. Whether the back or front face is visible is effectively determined after the polygon is projected onto the window. After this projection, if the polygon's edges are directed clockwise, one of the faces is visible; if directed counterclockwise, the other face is visible. Whether clockwise corresponds to front or back (and counterclockwise corresponds to back or front) is determined by the OpenGL programmer.

fade

  To modify the opacity and/or volume of a clip. A faded-up clip is unaffected, a clip faded down to 50% has 50% less opacity or volume, and a faded-down clip is completely transparent or completely turned off.

FDDI

  See fiber distributed data interface.

FDDI order

  In the computer world, the term bit order is analogous to the order for reading the flow of letters across a page of text. FDDI order is somewhat like reading from left to right, as English speakers normally do. Thus, the characters`TIME WAR` would be read as “time war.” To compare FDDI order to a very different ordering, see canonical order.

  In more technical terminology, FDDI order is a method for representing the 48-bit (6-byte) sequences used for addresses in FDDI. This method considers the first transmitted bit within a byte to be the most significant bit. For example, the sequence <1 followed by 0, 0, 0> is represented as 8 decimal. This is FDDI's native ordering and is bit-swapped within each byte with respect to canonical (or Ethernet) order. For the bytes themselves, the first transmitted byte is considered to be the most significant byte (the same as for canonical order).

  The SMT commands represent each byte of an FDDI address in FDDI order as a hexadecimal value (two hexadecimal characters) separated by a dash (-), for example, 10-00-96-25-30-0b. See also canonical order.

fiber distributed data interface (FDDI)

  A fiber distributed data interface that is a 100 Mb (megabits) per second standard for fiber optic communications made up of two counter-rotating rings of message traffic.

fiber optic cable

  A type of communications cable constructed of material (for example, glass) that allows an optical signal (light) to travel through it. Fiber optic cable currently is available in two types: multimode and single mode.

  The inside diameter, or pipe, of multimode fiber optic cable is big enough so that light “bounces off the walls” in a number of ways as it proceeds down the fiber. Each of the possible paths is referred to as a mode, and each takes a slightly different time to travel down the pipe. The existence of the multiple modes causes intersymbol interference.

  Single-mode fiber optic cable is narrower than multimode, so the transmitted signal bounces less. Only one mode (straight down the center) maintains its power and is low-loss. The other modes quickly dissipate as light moves down the fiber.

  The larger, multimode fiber optic cable (typically 62.5-micron internal diameter) is easier to launch a signal into. The interference, rather than the loss of power or spectral purity, limits the distance for a given bit rate, so multimode fibers are most often driven with inexpensive light emitting diodes (LEDs).

  The smaller, single-mode fiber (typically 50-micron internal diameter) is harder to couple power into. However, since there is only one mode, the light can travel much farther without successive bits interfering with one another—or, equivalently, a higher bit rate can be supported at a given distance. To achieve its higher potential, single-mode fiber is usually (but not always) driven with expensive semiconductor lasers rather than LEDs.

fiber optics

  A technology whereby signals are transmitted over an optical waveguide medium through the use of light-generating transmitters and light-detecting receivers.

field

  An area in a window in which you can type text.

field (in video systems)

  One of two (or more) equal parts of information in which a frame is divided in interlace scanning. A vertical scan of a frame carrying only its odd-numbered or its even-numbered lines. The odd field and even field make up the complete frame. See also frame, interlace.

field averaging

  A filter that corrects flicker by averaging pixel values across successive fields. See also flicker.

field blanking

  The blanking signals at the end of each field, used to make the vertical retrace invisible. Also called vertical blanking. See also vertical blanking, vertical blanking interval.

file

  A set of disk blocks in which you store information such as text, programs, or images you create using an application.

file descriptor

  A number returned by `open()` and other system functions to represent the state of an open file. The number is used with system calls such as `read()` to access the opened file or device.

file hierarchy

  See filesystem.

filesystem

  A hierarchical data structure that holds and organizes files in directories. Filesystems are designed so that users can find their files and organize them conveniently. Directories can contain other directories and files; files cannot contain directories or other files. The root (/) directory is at the top of the hierarchy.

fill

  For Token Ring networks (including 802.5 Token Ring and FDDI), a signal pattern placed on the transmission medium (cable) when a station is waiting.

filter

  To process a clip with spatial or frequency domain methods. Each pixel is modified by using information from neighboring (or all) pixels of the image. Filter functions include blur (low-pass) and crisp (high-pass).

flat shading

  Refers to coloring a primitive with a single, constant color across its extent, rather than smoothly interpolating colors across the primitive. See Gouraud shading.

flicker

  The effect caused by a one-pixel-deep line in a high-resolution graphics frame that is output to a low-resolution monitor, because the line is in only one of the alternating fields that make up the frame. This effect can be filtered out by field averaging. See also field, frame.

fog (OpenGL)

  A rendering technique that can be used to simulate atmospheric effects such as haze, fog, and smog by fading object colors to a background color based on distance from the viewer. Fog also aids in the perception of distance from the viewer, giving a depth cue.

font

  A group of graphical character representations usually used to display strings of text. The characters may be roman letters, mathematical symbols, Asian ideograms, Egyptian hieroglyphics, and so on.

form

  A window that contains buttons you click and/or editable fields you fill in.

forwarder

  The host that forwards mail from one domain to another.

fragment (in OpenGL)

  Fragments are generated by the rasterization of primitives. Each fragment corresponds to a single pixel and includes color, depth, and sometimes texture-coordinate values.

frame

  The result of a complete scanning of one image. In television, the odd field (all the odd lines of the frame) and the even field (all the even lines of the frame) make up the frame. In motion video, the image is scanned repeatedly, making a series of frames.

frame (FDDI)

  A protocol data unit (PDU) transmitted between cooperating MAC entities on a ring. (See also protocol data unit.) The nine fields of the FDDI frame and the number of symbols used by each field are: I=idle, SD=starting delimiter, FC=frame control, DA=destination MAC address, SA=source MAC address, data=user data, FCS=frame check sequence, ED=ending delimiter, and FS=frame status.

frame (Token Ring)

  The method for organizing information for communication among Token Ring stations and medium access control layers. There are three types of Token Ring frames: MAC frames, data frames, and the token.

frame class

  Identifies the general function of an FDDI frame. SMT defines eight frame classes: NIF (neighbor information frames), SIF (status information frames), ECF (echo frames), RAF (resource allocation frames), RDF (request denied frames), SRF (status report frames), PMF (parameter management frames), and ESF (extended service frames).

frame interval

  The inverse of frame rate, that is, the amount of time that a program has to prepare the next display frame. A frame rate of 60 Hz equals a frame time of 16.67 milliseconds. See also frame rate.

frame rate

  The frequency with which a simulator updates its display, in cycles per second (Hz). Typical frame rates range from 15 to 60 Hz.

Frame Scheduler

  The REACT/Pro Frame Scheduler is a process execution manager that schedules processes on one or more CPUs in a predefined, cyclic order. The scheduling interval is determined by a repetitive time base, usually a hardware interrupt.

frame type (FDDI)

  Defines the specific purpose of an FDDI frame. SMT frame types are Announcement, Request, and Response. Announcement communicates information; Request asks the targeted (destination) SMT to provide an answer; and Response is the answer to a Request frame. Each SMT frame class supports one, two, or three frame types.

framebuffer

  All the buffers of a given window or context. Sometimes includes all the pixel memory of the graphics hardware accelerator.

freeze, freeze-frame

  A condition on the digitized video signal where the digitizing is stopped and the contents of the signal appear frozen on the display or in the buffer. Sometimes used to capture the video data for processing or storage.

frequency

  The number of cycles completed by a signal in 1 second, expressed in hertz (Hz). For example, 5000 cycles per second is expressed as 5000 Hz (or 5 kHz).

frequency interlace

  Placing of harmonic frequencies of C signal midway between harmonics of horizontal scanning frequency Fh. Accomplished by making color subcarrier frequency exactly 3.579545 MHz. This frequency is an odd multiple of H/2.

front face

  See face.

front porch

  The portion of the video signal between the end of active video and the falling edge of sync. See also back porch, horizontal blanking, video waveform.

frs-master

  The process that creates a Frame Scheduler. The process's ID is used to identify the Frame Scheduler internally, so a process can be frs-master to only one scheduler.

frustum

  The view volume warped by perspective division.

G-Y signal

  Color mixture close to green, with a bandwidth 0.0 MHz to 0.5 MHz. Usually formed by combining B-Y and R-Y video signals.

gamma correction

  A function applied to colors stored in the framebuffer to correct for the nonlinear response of the eye (and sometimes of the monitor) to linear changes in color-intensity values.

gang scheduling

  A process scheduling discipline supported by IRIX version 5.3. The processes of a process group can request to be scheduled as a gang; that is, IRIX attempts to schedule all of them concurrently when it schedules any of them—provided there are enough CPUs. When processes coordinate using locks, gang scheduling helps to ensure that a process does not spend its whole time slice spinning on a lock held by another that is not running.

gateway

  A computer that, in addition to doing all the tasks that a router performs, supports conversion (translation) from one network's protocols to another's. For example, an FDDI/Ethernet gateway converts 4500-byte FDDI packets into 1500-byte Ethernet packets whenever packets originate on the FDDI ring and require routing (forwarding) to a destination on the Ethernet network. See also router.

genlocking

  Synchronizing with another video signal serving as a master timing source. The master timing source can be a composite video signal, a video signal with no active video (only sync information), or, for video studio, a device called house sync. When no master sync is available, VideoFramer, for example, can be set to “free run” (or standalone) mode, so that it becomes the master timing device to which other devices sync. See also line lock.

geometric model

  The object-coordinate vertices and parameters that describe an object. Note that OpenGL does not define a syntax for geometric models, but rather a syntax and semantics for the rendering of geometric models.

geometric object

  Geometric model.

geometric primitive

  A point, a line, or a polygon.

gizmo (in IRIS Showcase)

  IRIS Showcase groups sets of related commands and tools into gizmos. For example, all the tools that control paragraph formatting are in the Text Ruler gizmo. You access gizmos from the Gizmos menu.

Gouraud shading

  Smooth interpolation of colors across a polygon or line segment. Colors are assigned at vertices and linearly interpolated across the primitive to produce a relatively smooth variation in color. Also called smooth shading.

graphics object (in IRIS Showcase)

  An object you create using one of the 14 drawing tools available in IRIS Showcase.

gray-scale

  Monochrome or black-and-white, as in a monitor that does not display color.

grid (in IRIS Showcase)

  Rows of uniformly spaced vertical and horizontal dots you see in the IRIS Showcase drawing area. You can align objects to a grid.

group

  A collection of users who can set more relaxed permissions on files owned by one another.

group (in OpenGL)

  Each pixel of an image in client memory is represented by a group of one, two, three, or four elements. Thus, in the context of a client memory image, a group and a pixel are the same thing.

guaranteed latency

  For Token Ring networks (including 802.5 Token Ring and FDDI), the amount of time it takes for a signal to make a complete loop around the ring from the output port of one station around to the same station's input port. A ring with a small guaranteed latency is perceived as fast to its human users. The guaranteed latency of a ring increases as the trunk cable lengthens and as the number of stations increases. The ring's data speed also affects its guaranteed latency; the higher the data rate, the smaller the guaranteed latency.

guaranteed rate

  A rate of data transfer, in bytes per second, that definitely is available through a particular file descriptor.

H rate

  Number of complete horizontal lines, including trace and retrace, scanned per second.

half-space

  A plane divides space into two half-spaces.

handshake

  The protocol that controls the flow of information between a workstation and a printer. A hardware handshake uses only cable wires and pins to control the flow. A software handshake (also called xon-xoff flow control) uses a combination of pins, wires, and software.

hard guarantee

  A type of guaranteed rate that is met even if data integrity has to be sacrificed to meet it. See also guaranteed rate.

hard links

  When a new filename is linked to an existing file, the link made by default is a hard link. A hard link must be within the same filesystem as the original file. See symbolic link.

HDTV

  High-definition television. Though there is more than one proposal for a broadcast standard for HDTV, most currently available equipment is based on the 1125/60 standard, that is, 1125 lines of video, with a refresh rate of 60 Hz, 2:1 interlacing (same as NTSC and PAL), and aspect ratio of 16:9 (1920 x 1035 viewable resolution), trilevel sync, and 30 MHz RGB and luminance bandwidth.

heap

  The segment of the address space devoted to static data and dynamically allocated objects. Created by calls to the system function `brk()`. See also segment, address space.

Hi-8 mm

  An 8 mm recording format developed by Sony; accepts composite and S-Video signals.

highlight

  To change the color of an item on the screen by positioning the cursor over it (locate-highlight) or by positioning the cursor over it and pressing a mouse button.

home directory

  The directory into which IRIX places you each time you log in. It is specified in your login account; you own this directory and, typically, all its contents.

homogeneous coordinates

  A set of n+1 coordinates used to represent points in n-dimensional projective space. Points in projective space can be thought of as points in euclidean space together with some points at infinity. The coordinates are homogeneous because a scaling of each of the coordinates by the same nonzero constant does not alter the point to which the coordinates refer. Homogeneous coordinates are useful in the calculations of projective geometry, and thus in computer graphics, where scenes must be projected onto a window.

horizontal blanking

  The period when the electron beam is turned off, beginning when each scan line finishes its horizontal path (scan) across the screen.

horizontal blanking interval

  Also known as the horizontal retrace interval, the period when a scanning process is moving from the end of one horizontal line to the start of the next line. This portion of the signal is used to carry information other than video information. See also video waveform.

horizontal drive

  The portion of the horizontal blanking part of the video signal composed of the sync pulse together with the front porch and breezeway; that is, horizontal blanking minus the color burst. See also video waveform.

horizontal sync

  The lowest portion of the horizontal blanking part of the video signal; it provides a pulse for synchronizing video input with output. Also known as h sync. See also horizontal blanking, video waveform.

host

  Any system connected to the network.

hostname

  The name that uniquely identifies each host (system) on the network. The hostname is specified in the `/etc/sys_id` file. A system's hostname can be displayed with the `hostname` command.

hostname alias

  An optional, alternate hostname for a host (system) on the network.

HSI

  See hue-saturation-intensity.

HSV

  Hue-saturation-value. See hue-saturation-intensity.

hue

  The designation of a color in the spectrum, such as cyan, blue, magenta. Sometimes called tint on NTSC television receivers. The varying phase angles in the 3.58 MHz (NTSC) or 4.43 MHz (PAL) C signal indicate the different hues in the picture information.

hue-saturation-intensity

  A tristimulus color system based on the parameters of hue, saturation, and intensity (luminance). Also referred to as HSI or HSV.

hunt sequence

  A circular series of line settings such as different baud rates.

I signal

  Color video signal transmitted as amplitude modulation of the 3.58 MHz C signal (NTSC). The hue axis is orange and cyan. This signal is the only color video signal with a bandwidth of 0 to 1.3 MHz.

icon

  A small picture that represents a stowed or closed file, directory, application, or IRIX process.

Icon View window

  The window you see when you open a file folder (directory) icon. It displays the files, folders, and applications that the directory contains. To see an example of an Icon View window, from the Toolchest, choose Desktop > Access Files > In my Home Directory. You can control how the window displays icons by using options in the Sort, View, and Options menus, or by changing the settings in the Default Layout for Icon Views control panel (choose Desktop > Customize > Icon Views).

idle pattern

  See fill.

idle state

  For Token Ring networks (including 802.5 Token Ring and FDDI), a state of the ring where no data frames are being transmitted or repeated. Only the token and MAC frames are circling. This state is the opposite of the ring's active state.

IEEE order

  See canonical order.

image

  A rectangular array of pixels, either in client memory or in the framebuffer.

image plane

  See bitplane.

image primitive

  A bitmap or an image.

image processing

  Manipulating an image by changing its color, brightness, shape, or size.

immediate mode

  Execution of OpenGL commands when they're called, rather than from a display list. No immediate-mode bit exists; the mode in immediate mode refers to usage of OpenGL, rather than to a specific bit of OpenGL state.

import (in IRIS Showcase)

  To insert another file into IRIS Showcase. You can insert ASCII text files, images, 3D models, PICT files, and other IRIS Showcase files.

index

  A single value that's interpreted as an absolute value, rather than as a normalized value in a specified range (as is a component). Color indices are the names of colors, which are dereferenced by the display hardware using the color map. Indices are typically masked, rather than clamped, when out of range. For example, the index 0xf7 is masked to 0x7 when written to a 4-bit buffer (color or stencil). Color indices and stencil indices are always treated as indices, never as components.

inode (index node)

  An inode is a 128-byte data structure that the filesystem uses to store information about a file. The information in an inode includes the owner and access permissions, the size of the file, its file type, and the location of the information on the hard disk. There is one inode per file in the filesystem. The maximum number of files in a filesystem is limited by the number of inodes in that filesystem.

input focus

  Only one window at a time recognizes mouse movement and typing. The window that does is said to have the input focus.

insert

  For Token Ring networks (including 802.5 Token Ring and FDDI), the action taken by an attaching device by which it synchronizes its receive clock with the signal on the transmission medium (cable), verifies the uniqueness of its MAC address, and begins repeating the signal.

inst

  The software tool for installing system software, software options, and maintenance releases from SGI.

interchannel isolation

  The ability to prevent undesired optical energy from appearing in one signal path as a result of coupling from another signal path, thus eliminating crosstalk.

interlace

  A technique that uses more than one vertical scan to reproduce a complete image. In television, the 2:1 interlace used yields two vertical scans (fields) per frame: the first field consists of the odd lines of the frame, the other, the even lines. See also field, frame.

International Standards Organization (ISO)

  The international standardization body; ANSI represents the United States as a member of ISO.

internet

  A collection of packet-switching networks physically interconnected by IP gateways. “Internet” (with a capital “I”) is a wide-area network connecting many networks. The Internet network uses TCP/IP to transmit information.

Internet address

  A unique 4-byte (32-bit) number used by the Internet Protocol (IP or TCP/IP) software to identify computers (or more accurately, computers' network connections). Also called IP address.

interrupt

  A hardware signal from an I/O device that causes the computer to divert execution to a device driver.

interrupt latency

  The amount of time that elapses between the arrival of an interrupt signal and the entry to the device driver that handles the interrupt.

interrupt response time

  The total time from the arrival of an interrupt until the user process is executing again. Its three main components are interrupt latency, device service time, and context switch time. See also interrupt latency, device service time, context switch time.

IP address

  See Internet address.

IRE units

  A scale for measuring analog video signal levels, normally starting at the bottom of the horizontal sync pulse and extending to the top of peak white. Blanking level is 0 IRE units and peak white level is 100 IRE units (700 mv). An IRE unit equals 7.14 mv (+100 IRE to -40 IRE = 1v). IRE stands for Institute of Radio Engineers, a forerunner of the IEEE.

IRIS GL

  The SGI proprietary graphics library, developed from 1982 through 1992. OpenGL was designed with IRIS GL as a starting point.

IRIX

  The SGI version of the UNIX operating system. See system software.

IRIX processes

  Tasks that IRIX carries out to keep the system running correctly or to complete an explicit command. Each process has a unique process ID number.

ISO

  See International Standards Organization.

jaggies

  Artifacts of aliased rendering. The edges of primitives that are rendered with aliasing are jagged rather than smooth. A near-horizontal aliased line, for example, is rendered as a set of horizontal lines on adjacent pixel rows, rather than as a smooth, continuous line.

JK

  The nondata symbol pair that identifies the start of a Token Ring frame. See also symbol.

jot

  A mouse- and window-based text editor that is part of the base IRIX operating system software.

justify

  To line up text with the left and right margins.

KB (kilobyte)

  A standard unit for measuring the information storage capacity of disks and memory (RAM and ROM); 1024 bytes make one kilobyte (1 KB). Also kB, a standard unit for measuring telecommunication or network speeds; 1000 bits make one kilobyte (1 kB). For example, a 64 kBps ISDN line carries 64,000 bits per second, but a 64 KB disk has 65,536 bytes of memory.

keying

  Combining proportional amounts of two frames, pixel by pixel, with optional opacity. This process resembles taking two panes of glass with images on them and placing one pane on top of the other. The opacity of the top pane determines the parts of the bottom pane that show. Usually, keying is a real-time continuous process, as in the “over the shoulder” graphics in TV news programs. The alpha component of each pixel, which defines its opacity, determines how the images are combined. Combining images based on the alpha component is often called alpha keying or luma keying. See also compositing, mixing.

keyword

  A word that is automatically recognized by a program without the user having to declare or define the word in advance.

LAM

  See lobe attachment module.

latency

  For Token Ring networks (including 802.5 Token Ring and FDDI), a measurement of time during which a transmission medium (cable) is not available for use. See also guaranteed latency.

launch

  To start up an application, often by double-clicking an icon.

leading

  The amount of space between lines of text or between paragraphs. Leading is measured in points. Each point is 1/72nd of an inch.

leading edge of sync

  The portion of the video waveform after active video, between the sync threshold and the sync pulse. See also video waveform.

least significant

  The item in a sequence of symbols (for example, numerals or letters) that, by its placement within the sequence, makes the least difference in the value. For example, in the decimal number 209, nine is the least significant digit because it represents ones, while the other digits represent larger values (tens and hundreds). See also most significant.

LED (Light Emitting Diode)

  A light on a piece of hardware that indicates status or error conditions.

level

  Signal amplitude.

lighting (in OpenGL)

  The process of computing the color of a vertex based on current lights, material properties, and lighting-model modes.

line (in OpenGL)

  A straight region of finite width between two vertices. (Unlike mathematical lines, OpenGL lines have finite width and length.) Each segment of a strip of lines is itself a line.

line (in video systems)

  The result of a single pass of the sensor from left to right across the image.

line blanking

  The blanking signal at the end of each horizontal scanning line, used to make the horizontal retrace invisible. Also called horizontal blanking.

line frequency

  The number of horizontal scans per second, normally 15,734.26 times per second for NTSC color systems. The line frequency for the PAL 625/50H system is 15,625 times per second.

line lock

  Input timing derived from the horizontal sync signal, and implying that the system clock (the clock being used to sample the incoming video) is an integer multiple of the horizontal frequency and that it is locked in phase to the horizontal sync signal. See also video waveform.

line setting

  A set of line characteristics, such as expected rate of transmission (baud rate).

line state

  One of several characteristic patterns of bits or symbols transmitted on an FDDI fiber. See also symbol.

linear matrix transformation

  The process of combining a group of signals through addition or subtraction; for example, RGB signals into luminance and chrominance signals.

link (in IRIS Showcase)

  A mechanism for associating one piece of information with another. In IRIS Showcase you can link an object to another object, page, program, or file.

linked copy

  A pointer to a file or directory that exists in another location in the filesystem. When you make a linked copy of a file, you are not creating another instance of the file; you are creating another location from which you can access the original file.

live video

  Video delivered at a nominal frame rate appropriate to the format.

LLC

  See logical link control.

load

  The amount of traffic on the ring.

lobe

  For 802.5 Token Ring, the section (consisting of one or more segments) of cabling that connects an adapter to a trunk coupling unit (TCU).

lobe attachment module (LAM)

  For 802.5 Token Ring, a hardware device that acts as a concentrator (and trunk coupling unit), allowing one or more adapters to access the main (trunk) ring through it. LAMs may reside in a wiring closet and have lobe cabling that extends out to wall faceplate connections. See also lobe, concentrator.

local workstation

  The physical workstation whose keyboard and mouse you are using. All hardware connected to that workstation, and all software that resides on that hardware or its removable media, are also part of your local work area.

locality of reference

  The degree to which a program keeps memory references confined to a small number of locations over any short span of time. The better the locality of reference, the more likely a program executes entirely from fast cache memory. The more scattered a program's memory references, the higher the chance that it will access main memory or, worse, load a page from swap.

lock (in IRIS Showcase)

  An IRIS Showcase command that prevents you from accidentally moving or editing an object.

locks

  Memory objects that represent the exclusive right to use a shared resource. A process that wants to use the resource requests the lock that (by agreement) stands for that resource. The process releases the lock when it is finished using the resource. See also semaphore.

log in

  To give the system your login name so you can start a session on the system.

log out

  To end a session on the system.

logical link control (LLC)

  Local area network protocols in the lower layers of the OSI model. See also Open Systems Interconnection.

logical ring

  The set of MACs (for example, FDDI stations) serially connected, forming a single ring. An unwrapped, fault-free FDDI ring provides two logical rings.

logical volume

  A logical volume is a number of areas on one or more hard disks that the system considers as one filesystem. The fact that the areas of disk space are not contiguous is hidden from the user. See also striping.

login account

  A database of information about each user that, at the minimum, consists of login name, user ID, and home directory.

login name

  A name that uniquely identifies a user to the system.

login screen

  The window you see after powering on the system, before you can access files and directories. The window contains one icon for each login account on the system.

lost token

  For Token Ring networks (including 802.5 Token Ring and FDDI), a ring error condition. The condition exists when no station is transmitting and yet there is no token on the ring. The active monitor is responsible for correcting this error condition by regenerating the token.

luma

  See luminance.

luminance

  The perceived brightness of a surface. Typically refers to a weighted average of red, green, and blue color values that gives the perceived brightness of the combination. For video systems, luminance is the video signal that describes the amount of light in each pixel. See also chrominance, Y.

MII (M2)

  A second-generation recording format based on a version of the Y/R-Y/B-Y video signal. Developed by Panasonic, MII is also marketed by other video manufacturers. Though similar to Betacam, it is nonetheless incompatible.

MAC

  See media access control.

MAC address

  Also called the physical address. An address that uniquely identifies the medium access control module of a station. In 802.5 environments, this is a 2-byte (16-bit) or 6-byte (48-bit) address. In FDDI environments, this is a 6-byte address. There is one MAC address for each network adapter on the ring. All the adapters on a ring must use the same address format: either the 2-byte format or the 6-byte one. MAC addresses can be universally assigned (UAA), in which case they are guaranteed to be globally unique, or they can be locally assigned (LAA), in which case they are unique only to their particular ring (or site). LAA MAC addresses (both 2-byte and 6-byte formats) are usually assigned and administered by a site's network manager. Blocks of UAA MAC addresses (6-byte format only) are assigned by the Institute of Electrical and Electronics Engineers (IEEE). (The IRIS Token Ring product supports only the 6-byte format for MAC addresses.)

MAC frames

  Token Ring frames that contain management information in the “Information” segment. MAC frames are used to monitor and manage the ring. The frames are generated and interpreted by the medium access control sublayer (MAC) on each network interface board. The information exchanged with these frames is used by each station's monitor module.

maintenance release

  A software release that contains bug fixes to system software and software options. Occasionally, a maintenance release contains feature enhancements or support for new hardware.

major frame

  The basic frame rate of a program running under the Frame Scheduler.

man page

  See reference page.

management frames

  See MAC frames.

management information base (MIB)

  A database of FDDI station and ring information. Each Station Management (SMT) module manages its own MIB. However, in order to manage the ring, SMTs share much of the MIB information with one another. Each MIB object (item of information) has a set of attributes, including read/write permissions. FDDIXPress provides the `/usr/etc/smtstat` command to display MIB information.

map

  Numerical lookup of pixel data that modifies each pixel without using neighboring pixels. This large category of video editing functions includes clip/gain, solarization, and histogram equalization.

matrix

  A two-dimensional array of values. OpenGL matrices are all 4×4, though when they are stored in client memory they're treated as 1×16 single-dimension arrays.

matrix transformation

  The process of converting analog color signals from one tristimulus format to another, for example, RGB to YUV. See also tristimulus color system.

MAU

  See multistation access unit.

MB (megabyte)

  A standard unit for measuring the information storage capacity of disks and memory (RAM and ROM); 1024 kilobytes make one megabyte (1 MB). Also a standard unit for measuring network or telecommunications speeds; 1000 kilobytes make one megabyte.

media access control (MAC)

  Local area network protocol functions corresponding to the OSI data link layer (layer 2). MACs manage data link layer communication. On transmission, they assemble data into a frame with address and error-detection fields. On reception, they disassemble frames and perform address recognition and error detection.

media interface connector (MIC)

  A type of connector that provides an interface (connection) between FDDI cables. Each MIC contains two fiber optic fiber lines: one for transmit and one for receive.

memory intensive

  A program is said to be memory intensive if it uses a great deal of memory and performs frequent changes to the data in memory so that the system cannot swap out the data to allow other processes to use the memory. For example, word processing applications with many open files use a great deal of memory.

menu

  A list of operations or commands that the system can carry out on various objects on the screen.

MIB

  See management information base.

MIC

  See media interface connector.

MIC receptacle

  The fixed or stationary half of an optical signal transmissions cable connection attached to FDDI. Receptacles mate with plugs. See also connector receptacle.

minimize

  To shrink a window and display it as a stowed icon on the screen. Minimized applications continue to run.

minor frame

  The scheduling unit of the Frame Scheduler. The period of time in which any scheduled process must do its work.

mixing

  In video editing, combining two clips frame by frame, pixel by pixel. Usually, a linear interpolation between the pixels in each clip is used, with which you can, for example, perform a cross-fade. Other operations include averaging, adding, differencing, maximum (non-additive mix), minimum, and equivalence (white where equal, else black). See also compositing, keying.

mode

  The characteristics of the terminal interface. A part of line settings. The TTY line and the terminal must be working in the same mode before communication can take place.

modelview matrix

  The 4×4 matrix that transforms points, lines, polygons, and raster positions from object coordinates to eye coordinates.

monitor

  The device that displays the image in the framebuffer.

monitor (Token Ring)

  A software module within each Token Ring station that maintains and manages the ring and recovers from various error situations. Only one monitor on a ring is active; all other monitors are standby.

most significant

  The item in a sequence that, by its placement within the sequence, makes the most difference in the value. For example, in the decimal number 209, two is the most significant digit because it represents hundreds while the other digits represent smaller values (tens and ones). See also least significant.

motion blurring (in OpenGL)

  A technique that simulates what you get on a piece of film when you take a picture of a moving object, or when you move the camera when you take a picture of a stationary object. In animations without motion blur, moving objects can appear jerky.

mount

  To make a filesystem that is stored on a local or remote disk resource accessible from a specific directory on your workstation.

mount point

  The directory on your workstation from which you access information that is stored on a local or remote disk resource. Most mount point directories are left empty because information in that directory is unavailable while the filesystem is mounted there.

mouse

  A hardware device you use to communicate with windows and icons. You move the mouse to move the cursor on the screen, and you press its buttons to initiate operations. An optical mouse must always be on the mouse pad for the system to interpret its movements; a mechanical mouse works on any clean, flat surface.

mouse pad

  For an optical mouse, this is the rectangular, metallic surface that reads the movements of the mouse. For a mechanical mouse, this is a clean, soft rectangular surface that makes the mouse's track ball roll efficiently.

movie

  A file you create and view on your workstation screen.

multiburst

  A test pattern consisting of sets of vertical lines with closer and closer spacing; used for testing horizontal resolution of a video system.

multistation access unit (MAU)

  For 802.5 Token Ring, a hardware device that acts as a concentrator (and trunk coupling unit), allowing one or more adapters to access the main (trunk) ring through it. MAUs may reside in a wiring closet and have lobe cabling that extends out to wall faceplate connections. See also lobe, concentrator.

multi-tasking system

  A system that can run several processes (such as running applications, printing files, and updating files) simultaneously.

multiuser system

  A system that several users can work on simultaneously and maintain private files.

neighbor

  The two functioning stations on either side of an FDDI station. A neighbor station is the immediate next station on a logical ring when viewed from the station in question. A neighbor can be either upstream or downstream. See also upstream, downstream, logical ring.

neighborhood information frame (NIF)

  The frame used by an FDDI station for periodic announcement of its address and basic station description.

network

  Two or more computers and other devices (such as printers) that can communicate with one another electronically to transfer and share information.

network address

  A unique, nonphysical address that identifies a local area network.

network connection name

  A user-friendly name associated with a specific network interface. Network connection names are specified in the`/etc/hosts` file. The network connection name for the primary network interface is the system's hostname. (See hostname.) By convention, a system's other network connection names include the system's hostname.

network administrator

  The individual(s) responsible for setting up, maintaining, and troubleshooting the network, and for supplying setup information to system administrators of each system.

Network Information Center

  The central authority that assigns blocks of Internet Protocol (IP) addresses to worldwide public and private organizations. See also Internet address.

NFS

  A networking software option that lets you access files and directories that reside on the disks of other workstations as if they resided on a local disk in your own workstation. NFS stands for Network File System.

NIF

  See neighborhood information frame.

NIS

  A networking software option that lets you control network information and services from a central server called the NIS master. NIS stands for Network Information Service. See also centralized network, NIS client, NIS domain, NIS master.

NIS client

  A system on a centralized network— other than the NIS master—that runs NIS. The NIS client receives services and information from the NIS master.

NIS domain

  The unique name of a network (or subnetwork) that runs NIS. All hostnames in the NIS domain have the NIS domain name as their suffix.

NIS master

  The server that stores the complete database of information about all the hosts (systems) and users on a centralized NIS network. The NIS master periodically updates host information on all other systems on the network (NIS clients); its user information is always available to every host. The network administrator is responsible for setting up, maintaining, and troubleshooting the NIS master.

node (networking)

  A generic term referring to any device attached to the network. All nodes must have at least one physical layer address (for example, a MAC address). However, not all nodes have network layer addresses; user data cannot be sent to nodes that do not have network addresses. A bridge is an example of a node without a network address; a station is a node with a network layer address. For FDDI, there is only one SMT module managing each node, regardless of the number of MAC, PMD, or PHY components the node has.

nonconvex

  A polygon is nonconvex if there exists a line in the plane of the polygon that intersects the polygon more than twice.

normal

  A three-component plane equation that defines the angular orientation, but not position, of a plane or surface.

normalize

  Divide each of the components of a normal by the square root of the sum of their squares. Then, if the normal is thought of as a vector from the origin to the point (nx', ny', nz'), this vector has unit length.

  factor = (nx2 + ny2 + nz2)1/2

  nx' = nx / factor

  ny' = ny / factor

  nz' = nz / factor

normal vector

  Same as normal.

notifier

  A form that appears on screen when the system requires that you confirm an operation you just requested, or when an error occurs.

NTSC

  A color television standard or timing format encoding all of the color, brightness, and synchronizing information in one signal. Used in North America, most of South America, and most of the Far East, this standard is named after the National Television Systems Committee, the standardizing body that created this system in the U.S. in 1953. NTSC uses a total of 525 horizontal lines per frame, with two fields per frame of 262.5 lines each. Each field refreshes at 60 Hz (actually
  59.94 Hz).

null modem

  A type of cable that reverses the wires on which information is sent and received. Some devices receive and send information on opposite wires, and you must switch these wires to use the devices properly.

NURBS

  Non-Uniform Rational B-Spline. A common way to specify parametric curves and surfaces.

Nyquist limit

  The highest frequency of input signal that can be correctly sampled without aliasing. The Nyquist limit is equal to half of the sampling frequency.

object (in OpenGL)

  An object-coordinate model that's rendered as a collection of primitives.

object coordinates

  Coordinate system prior to any OpenGL transformation.

object (in IRIS Showcase)

  Everything you place on the page in an IRIS Showcase file is considered an object—the graphics you draw, text you type, and images and 3D models you import.

octet

  A data unit composed of eight ordered bits; octet is a synonym for byte. A pair of data symbols is represented in one octet.

offset

  In the context of a video signal, the relative coordinates from the upper left corner of the video image where signal sampling begins.

opacity (in IRIS Showcase)

  An IRIS Showcase setting that determines whether objects are opaque or see-through.

open

  To double-click an icon, or to select an icon then choose “Open” from a menu to display a window that contains the information that the icon represents.

Open Systems Interconnection (OSI)

  The OSI model is a standard for computer communications protocols and the implementation of these protocols. The model is a product of International Standards Organization (ISO) and specifies a seven-layer architecture.

OpenGL

  OpenGL is a graphics library—a software interface to graphics hardware—based on IRIS GL and developed by SGI with an industry consortium known as the OpenGL Architecture Review Board. This interface consists of about 120 distinct commands (plus associated constants and variables), which you use to specify the objects and operations needed to produce interactive 3D applications. The term OpenGL can also refer to the hardware-independent specification for the OpenGL graphics library.

optical bypass switch (OBS)

  A device that can be connected between a dual-attachment station and the dual-ring of an FDDI local area network. If the station fails, is powered down, or is physically removed, the OBS prevents the ring from wrapping by directing the signal back onto the ring, thus bypassing the station. The station's two neighbors notice that their upstream/downstream neighbor has changed, but the signal continues to loop around the ring, so no wrap occurs.

orthographic

  Nonperspective projection, as in some engineering drawings, with no foreshortening.

OSI

  See Open Systems Interconnection.

overrun

  When incoming data arrives faster than a data collection system can accept it, so that data is lost, an overrun has occurred. See also underrun exception.

overrun exception

  When a process scheduled by the Frame Scheduler should have yielded before the end of the minor frame and did not, an overrun exception is signaled.

overscan

  To scan a little beyond the display raster area of the monitor so that the edges of the raster are not visible. Television is overscanned; computer displays are underscanned.

owner

  The user who created a particular file or directory and who can specify which other users of the system can access the file.

page fault

  The hardware event that results when a process attempts to access a page of virtual memory that is not present in physical memory.

page notes (in IRIS Showcase)

  Each page in an IRIS Showcase file can have a separate page of notes associated with it. You create page notes using the Page Notes command.

pages

  The units of real memory managed by the kernel. Memory is always allocated in page units on page-boundary addresses. Virtual memory is read and written from the swap device in page units.

PAL

  A color television standard or timing format developed in West Germany and used by most other countries in Europe, including the United Kingdom but excluding France, as well as Australia and parts of the Far East. PAL uses a total of 625 horizontal lines per frame, with two fields per frame of 312.5 lines per frame. Each field refreshes at 50 Hz. PAL encodes color differently from NTSC. PAL stands for Phase Alternation Line or Phase Alternated by Line, by which this system attempts to correct some of the color inaccuracies in NTSC. See also NTSC, SECAM.

paragraph

  The elements between carriage returns. A paragraph can be one character, one word, or several pages.

paragraph format

  The leading, tab settings, margin settings, and justification for a paragraph. In an IRIS Showcase file, you control these with the Text Ruler gizmo.

parallel port

  An outlet on the workstation to which you connect external printers and similar devices.

parameter (in OpenGL)

  A value passed as an argument to an OpenGL command. Sometimes one of the values passes by reference to an OpenGL command.

parent directory

  A relative term that refers to a directory that contains another directory. If directory A contains directory B, then A is the parent directory of B.

password

  A combination of letters and/or numbers that only you know that allows you access to a system. A password is an optional element of your login account. If you specify a password for your account, you must type it after you type your login name before the system lets you access files and directories.

path

  A list of directories the system searches when trying to find a file or run a program. You can add directories to and delete directories from your path.

path test

  A self-test performed by an FDDI node's own CMT to verify that its connection to the ring is performing correctly. The path test is one part of the trace function.

pathname

  The list of directories that leads you from the root (/) directory to a specific file or directory in the filesystem.

pathway

  In the Video Library, a connection of sources and drains that provide useful processing of video signals. Pathways have controls and video streams. Pathways can be locked for exclusive use, and are the target of events generated during video processing. See also exclusive use, event.

pattern palette (in IRIS Showcase)

  The collection of patterns that you can use in IRIS Showcase.

PCM

  See physical connection management.

PDU

  See protocol data unit.

peak data rate

  The instantaneous maximum rate of input to a data collection system. The system must be able to accept data at this rate to avoid overrun. See also average data rate, overrun.

pedestal

  See setup and video waveform.

peripheral

  A hardware device that adds more functionality to the basic workstation, such as a tape drive. See also external device.

permission

  The information attached to each directory and file that specifies which users can access it and to what degree.

permissions mask

  A system setting that specifies the default permissions that the system assigns to newly created files and directories. The owners of those files and directories can later change the permissions.

perspective division

  The division of x, y, and z by w, carried out in clip coordinates.

PHY

  See physical layer protocol.

physical connection management (PCM)

  The portion of connection management (CMT) that manages a physical connection between the PHY being managed and another PHY, likely an adjacent (neighbor) station on the ring.

physical layer protocol (PHY)

  The layer that performs the clock recovery and serial-to-parallel (receive) or parallel-to-serial (transmit) conversion of data between the transmission medium and the MAC entity.

physical layer medium dependent protocol (PMD)

  The medium that specifies the optical-to-electrical conversion mechanism to conform to FDDI.

pin (in IRIS Showcase)

  An IRIS Showcase command that prevents you from accidentally moving an object.

pixel

  Picture element. Either the smallest addressable spatial element of the computer screen, or the smallest reproducible element in analog video. A pixel can have red, blue, and green color values, an alpha component, and other information associated with it. (Pixels are referred to as having a color component even if they're gray-scale or monochrome.) The bits at location (x, y) of all the bitplanes in the framebuffer constitute the single pixel (x, y). In OpenGL window coordinates, each pixel corresponds to a 1.0x1.0 screen area. The coordinates of the lower left corner of the pixel named x,y are (x, y), and of the upper right corner are (x+1, y+1). See also alpha value, component video.

pixel map

  A two-dimensional piece of memory, any number of bits deep. See also bitmap.

PMD

  See physical layer medium dependent.

point (in OpenGL)

  An exact location in space, which is rendered as a finite-diameter dot.

point

  A unit for measuring font size and leading. One point is 1/72nd of an inch.

polygon

  A near-planar surface bounded by edges specified by vertices. For example, each triangle of a triangle mesh is a polygon, as is each quadrilateral of a quadrilateral mesh. The rectangle specified by glRect*() is also a polygon.

pop

  To bring to the foreground, that is, to the top of the stack, a window or object that is in the background, or lower in the stack. Windows on the screen and objects in the IRIS Showcase drawing area can overlap one another. You can pop a window so it appears on top of other windows; you can pop an object so it appears on top of other objects. See push.

port

  A physical point of attachment where a computer's signals pass through to a peripheral device or a communications network medium (for example, a cable). A port has a built-in connector. The type of connector depends on the port's use. For example, Ethernet 10Base-T ports use RJ-11 connectors; FDDI ports use MIC connectors; many printers use SCSI connectors; modem ports use RJ-45 connectors.

  For FDDI, there are four classes of ports: A, B, S, and M. Ports A and B are both used for a dual-attachment configuration; port S (or port A) is used for a single-attachment configuration; M ports are for single-attachment station connections and are found only on concentrators. Each FDDI port has both an incoming (reception) line and an outgoing (transmission) line; however, in some configurations, only one line is in use.

postproduction

  The processes that occur before release of the finished video product, including editing, painting (2D graphics) production, and 3D graphics production.

power cable

  The cable that connects the workstation to a grounded electrical outlet.

power off

  To turn off the power switches on the workstation chassis and the monitor. You should power off the system only after using the system shutdown procedure. See shut down.

power on

  To turn on the power switches on the workstation chassis and the monitor.

primary colors

  Red, green, and blue. Opposite voltage polarities are the complementary colors cyan, magenta, and yellow.

primary ring

  The main transmission ring within an FDDI dual ring. See also dual-attachment station, secondary ring.

primitive

  A point, a line, a polygon, a bitmap, or an image. (Note: Not just a point, a line, or a polygon!)

Print Manager

  A tool that you use to set up printer software and monitor jobs that you send to the printer. You access it through either the System toolchest or the System Manager, where it is called the Printer tool.

priority

  A method for indicating the relative urgency or importance of data. Token Ring provides eight levels of priority and a set of rules for ensuring that higher-priority data is transmitted before lower-level data

priority field

  For 802.5 Token Ring, a sequence of bits (a field) within the access control portion of each token that is used to indicate the ring's current priority level. Stations can transmit data that has the same or a higher priority level than the level indicated in the token's priority field. Data with a lower priority must wait for the ring's priority level to decrease.

process

  The entity that executes instructions in a UNIX system. A process has access to an address space containing its instructions and data. The state of a process includes its set of machine register values, as well as many process attributes. See also address space, process attributes.

process attributes

  Variable information about the state of a process. Every process has a number of attributes, including its machine register contents, process ID, user and group IDs, working directory, open file handles, scheduler class, and environment variables.

process group

  See share group.

processor sets

  Groups of one or more CPUs designated using the `pset` command.

programmed I/O (PIO)

  Transfer of data between memory and an I/O device in byte or word units, using program instructions for each unit. Under IRIX, I/O to memory-mapped VME devices is done with PIO. See DMA.

projection matrix

  The 4×4 matrix that transforms points, lines, polygons, and raster positions from eye coordinates to clip coordinates.

PROM monitor

  The interface for communicating with the system after it is powered up, but before it is booted up and running IRIX.

prompt

  A character or word that the system displays in an IRIX shell that indicates the system is ready to accept commands. The default prompt for regular user accounts i`s %`; the default prompt for the root account is `#`.

protocol data unit (PDU)

  The unit of data transfer between communicating peer layer entities. It may contain control information, address information, data, or any combination of the three. See also frame.

purge

  For 802.5 Token Ring, to clear the ring of all signals. This is one of the first actions performed by the active monitor upon taking on its role.

push

  To put to the background, that is, lower in the stack, a window or object that is in the foreground, or the top of the stack. Windows on the screen and objects in the IRIS Showcase drawing area can overlap each other. You can push a window so it hides behind other windows; you can push an object so it appears below other objects. See pop.

Q signal

  The color video signal that modulates 3.58 MHz C signal in quadrature with the I signal. Hues are green and magenta. Bandwidth is 0.0 MHz to 0.5 MHz. See also C signal, I signal, YC, YIQ.

quadrilateral

  A polygon with four edges.

quantization error

  The magnitude of the error introduced in a signal when the actual signal is between levels, resulting from subdividing a video signal into distinct increments, such as levels from 0 to 255.

queue

  A list of print jobs waiting to be printed on a particular printer.

quit

  To stop running an application.

R-Y (R minus Y) signal

  A color difference signal obtained by subtracting the luminance signal from the red camera signal. It is plotted on the 90 to 270 degree axis of a vector diagram. The R-Y signal drives the vertical axis of a vectorscope. The color mixture is close to red. Phase is in quadrature with B-Y; bandwidth is 0.0 MHz to 0.5 MHz. See also luminance, B-Y (B minus Y) signal, Y/R-Y/B-Y, vectorscope.

race condition

  Any situation in which two or more processes update a shared resource in an uncoordinated way. For example, if one process sets a word of shared memory to 1, and the other sets it to 2, the final result depends on the “race” between the two to see which can update memory last. Race conditions are prevented by use of semaphores or locks. See also semaphores, locks

raster

  The scanning pattern for television display; a series of horizontal lines, usually left to right, top to bottom. In NTSC and PAL systems, the first and last lines are half lines.

raster operation, raster op

  A logical or arithmetic operation on a pixel value.

rasterize

  To convert a projected point, line, or polygon, or the pixels of a bitmap or image, to fragments, each corresponding to a pixel in the framebuffer. Note that all primitives are rasterized, not just points, lines, and polygons.

receive

  The action of a station accepting a token, frame, or other symbol sequence from the incoming medium.

receiver

  An electronic circuit that converts an optical signal to an electric logic signal.

rectangle

  A quadrilateral whose alternate edges are parallel to each other in object coordinates. Polygons specified with glRect*() are always rectangles; other quadrilaterals might be rectangles.

reference page

  An online document that describes how to use a particular IRIX command. Also called man page.

registration

  The process of causing two frames to coincide exactly. In component video cameras or displays, the process of causing the three color images to coincide exactly, so that no color fringes are visible.

remote workstation

  A workstation you can access across the network; it is not physically connected to your workstation. All hardware connected to that workstation, and all software that resides on that hardware or its removable media, are also part of that remote work area.

rendering

  Conversion of primitives specified in object coordinates to an image in the framebuffer. Rendering is the primary operation of OpenGL—it's what OpenGL does.

repeat

  For Token Ring networks (including 802.5 Token Ring and FDDI), the act of reading a signal from the transmission medium (cable) and retransmitting it. Every Token Ring station is required to constantly do this, except when it is in the bypass state or when it is transmitting data. When repeating a frame, a station may alter the settings on some of the bits (for example, the reservation field, the A bit, the C bit). See also repeater.

repeater

  A hardware device that repeats back onto the ring each signal it receives (reads) from it. Each attaching device on a Token Ring must be connected to its own repeater; the repeater is usually located on the network adapter board.

  In some contexts, this term refers to a special node used only for boosting the ring's signal, which enables lengthening the geographical distance covered by a network.

reservation field

  For 802.5 Token Ring, a sequence of bits (a field) within the access control field of each frame (data, MAC, or token) that is used to indicate a desired priority level. When a station has higher-priority data to transmit, it indicates the desired priority level in the reservation field of any frame that it is repeating. Sometime later (governed by the priority mechanism), a token is generated with the requested priority level.

reset button

  A physical button on the workstation that, when pressed, cuts off then immediately restores power to the workstation. Pressing the reset button does not turn off power to the option slot devices. Never press the reset button while IRIX is running, unless all attempts to shut down the system using software fail. See also shut down.

resident set size

  The aggregate size of the valid (that is, memory-resident) pages in the address space of a process. Reported by `ps`(1) under the heading RSS. See also virtual size.

resolution

  Number of horizontal lines in a television display standard; the higher the number, the greater a system's ability to reproduce fine detail.

restore (files)

  To copy files that once resided on a hard disk from another disk or a tape back onto the hard disk.

RGB

  Red, green, blue—the basic component set used by graphics systems and some video cameras in which a separate signal is used for each primary color.

RGB format

  The technical specification for NTSC color television. Often (incorrectly) used to refer to an RGB signal that is being sent at NTSC composite timings, for example, an SGI computer set to output 640 x 480. The timing is correct to display on a television, but the signal is still split into red, green and blue components. This component signal would have to go through an encoder to yield a composite signal (RS-170A format) suitable for display on a television receiver.

RGBA

  Red, Green, Blue, Alpha.

RGBA mode

  An OpenGL context is in RGBA mode if its color buffers store red, green, blue, and alpha color components, rather than color indices.

ring

  Two or more stations (specifically repeaters) connected by transmission media (cabling) in a manner such that the signal travels from repeater to repeater in a closed loop, returning to the original transmitting station after all other active stations on the ring have seen the signal. Each station examines all information on the physical medium, copies information that is addressed to it, and returns all the information to the medium, where the originating station recognizes the data as its own and removes it. A number of connection schemes can be used to construct a ring.

ring management (RMT)

  The portion of connection management that monitors the MAC in a Token Ring local area network. It provides a trace mechanism to handle beaconing and also detects duplicate addresses on the ring.

RMT

  See ring management.

root account

  The standard IRIX login account reserved for use by the system administrator. This account's home directory is the root (/) directory of the filesystem; the user of the root account has full access to the entire filesystem (that is, can change and delete any file or directory). The user of this account is sometimes referred to as the superuser.

root (/) directory

  The directory at the top of the filesystem hierarchy.

round-robin

  A scheme for controlling action in which all the devices in a circle take turns sequentially. In local area networks, the controlled action is permission to transmit data onto the transmission medium (cable) that is laid out as a ring. At any point in time, only one station has the permission (the turn). When the turn-taker finishes transmitting, it passes the turn (token) to the next downstream entity. This system guarantees that only one station at a time is transmitting and that each station is given a turn.

route

  Also referred to as a link. A group of addresses on a network that define a path from one station (the source address) to another station (the destination address). Each address within a route provides the next step along that route. And, each address for an intermediate station is a where the packet stops (is picked up) and is transferred to another local area network. A complete route from source to destination may consist of one or numerous addresses. In Token Ring, routes are limited to a maximum of 7 addresses.

router

  Also referred to as intermediate system. A computer, with connections to two or more networks, that routes (forwards) packets between two or more networks and is capable of discovering (or maintaining) routes to distant network destinations. In the simplest situation, a router with two network connections moves, from network 1 to network 2, all of the packets that have been transmitted on network 1, but are destined for a host on network 2, and vice versa. In cases in which the destination host is located on a network to which the router is not physically attached, the router sends the packet to the next router along the route, and that router passes the packet to another router, until the packet can be delivered directly to the specified destination host. In OSI terminology, a router is an Intermediate System supporting network layer forwarding.

routing

  The process of discovering and assigning a route from a sending computer (the source address) to an intended receiving computer (the destination address). The routing method used for any particular packet/datagram can be either source routing or transparent routing. The exact manner in which routing is done differs from protocol to protocol.

  In Token Ring environments, source routing at the medium access control sublayer is a major routing method. Each station maintains the routing information for all the stations with which it wishes to communicate. Each route (or link) consists of one to seven addresses that, when followed sequentially, leads to the destination. The number of routes that a particular station (or adapter) can handle depends on the amount of memory available.

  In Ethernet environments, routing is handled by the upper layers of the protocol stack (for example, the Exterior Gateway Protocol, the Routing Information Protocol, the source routing option in the Internet Protocol). For BSD UNIX environments (including IRIX) using the TCP/IP protocol, both source and transparent routing are available. Software modules acting as routers and gateways maintain the routing information and handle transparent routing. There is virtually no limit to the number of addresses that can be specified in a source route; however, there is a practical limit set by available memory.

SA

  See source address.

sample

  To read the value of a signal at evenly spaced points in time; to convert representational data to sampled data (that is, synthesizing and rendering).

sampling rate

  The number of times per second (measured in kHz, where
  1 kHz = 1000 times per second) the system reads the file when outputting audio. The greater the sampling rate, the larger the file and the better the quality of the audio output.

saturation

  Color intensity; zero saturation is white (no color) and maximum saturation is the deepest or most intense color possible for that hue. In signal terms, saturation is determined by the ratio between luminance level and chrominance amplitude. See also hue.

scaling

  To change the size of an image.

scan

  To convert an image to an electrical signal by moving a sensing point across the image, usually left to right, top to bottom.

schemes

  A scheme is a pre-packaged collection of colors and fonts that users can apply to application windows. Having all applications on a workstation use schemes allows users to conveniently customize their environment. The schemes are designed with an eye to effective use of color, taking into account both usability and aesthetic considerations. Multiple schemes are provided to address issues such as red-green colorblindness, monochrome X-terminals, and user preference for light or dark text. A user changes the scheme for the desktop simply by selecting the new scheme from a control panel.

screen

  The portion of the monitor that displays information.

SCSI

  Small Computer System Interface (pronounced “scuzzy”). SCSI is a high-speed input/output specification for small computers.

SCSI address

  A number from one to seven that uniquely identifies a SCSI device to a system. No two SCSI devices that are physically connected to the same SCSI bus can have the same SCSI address.

SCSI address dial

  A small plastic dial connected to some SGI external SCSI devices. You click on its small buttons to select a SCSI address for a new SCSI device.

SCSI bus length

  The combined length of all internal and external SCSI cables in a system for each SCSI bus.

SCSI cable

  A cable that connects a SCSI device to a SCSI port on a workstation.

SCSI device

  A hardware device that uses the Small Computer System Interface (SCSI) protocol to communicate with the system. Hard disk, floppy disk, CD-ROM, and tape drives are all SCSI devices.

SCSI terminator

  An electronics device, often an external plug, that is required at the end of each SCSI bus.

SECAM

  Sequentiel Couleur avec Memoire, the color television system developed in France and used there as well as in eastern Europe, the Near East and Mideast, and parts of Africa and the Caribbean.

secondary ring

  The backup ring used when a fault occurs on the primary ring of an FDDI local area network. See also primary ring.

segment

  Any contiguous range of memory addresses. Segments as allocated by IRIX always start on a page boundary and contain an integral number of pages.

select an icon

  To position the cursor over an icon then click the (left) mouse button. Once an icon is selected, it is the object of whatever operation you select from a menu.

semaphore

  A memory object that represents the availability of a shared resource. A process that needs the resource executes a “p” operation on the semaphore to reserve the resource, blocking if necessary until the resource is free. The resource is released by a “v” operation on the semaphore. See also locks.

sequential alignment (in IRIS Showcase)

  A method of aligning objects in IRIS Showcase that lets you create uniform spacing between the bottom of one object and the top of another or the right edge of one object and the left edge of another.

serial device

  A hardware device that requires a serial cable connection to communicate with the workstation.

serial port

  An outlet on the workstation to which you connect external serial devices.

server (in OpenGL)

  The computer on which OpenGL commands are executed. This might differ from the computer from which commands are issued. See client.

server

  A system that other systems on the network access to use its disk space, software, or services.

server administrator

  The person who is responsible for keeping the server system up and running. This person is often also a site administrator.

setup

  The difference between the blackest level displayed on the receiver and the blanking level. A black level that is elevated to 7.5 IRE instead of being left at 0.0 IRE is the same as the lowest level for active video. Because the video level is known, this part of the signal is used for black-level clamping circuit operation. Setup is typically used in the NTSC video format and is typically not used in the PAL video format; it was originally introduced to simplify the design of early television receivers, which had trouble distinguishing between video black levels and horizontal blanking. Also called pedestal. See also video waveform.

SGI workstation

  Any graphics workstation manufactured by SGI.

shading

  The process of interpolating color within the interior of a polygon, or between the vertices of a line, during rasterization.

share group

  A group of two or more processes created with `sproc()`, including the original parent process. Processes in a share group share a common address space and can be scheduled as a gang (see gang scheduling). Also called a process group. See also gang scheduling

shell

  A window into which you type IRIX commands. The syntax of the commands depends on the type of shell you are using, such as the C shell or Bourne shell.

shell script

  A program that issues and interprets a sequence of IRIX commands.

shielded cable

  A cable with a protective covering that reduces the possibility of interference with radio, television, and other devices.

shuffle

  To change the order in which windows are stacked on the screen.

shut down

  To safely close all files, log out, and bring the workstation to a state where you can safely power it off. Choose “System Shutdown” from the System toolchest menu to do this.

SIF

  See status information frame.

signal latency

  The time that elapses from the moment a signal is generated until the signal-handling function begins to execute. Signal latency is longer, and much less predictable, than interrupt latency. See also interrupt latency.

SIMM

  A small printed circuit board with DRAM (dynamic random-access memory) chips.

single-attachment station (SAS)

  A station that offers a single connection (attachment) to the FDDI network.

single-buffering

  OpenGL contexts that do not have back color buffers are single-buffered. You can use these contexts for animation, but take care to avoid visually disturbing flashes when rendering.

singular matrix

  A matrix that has no inverse. Geometrically, such a matrix represents a transformation that collapses points along at least one line to a single point.

site administrator

  The person responsible for maintaining systems and the network at a site. A site is the area covered by the local network of systems.

smear

  An artifact usually caused by mid-frequency distortions in an analog system that results in the vertical edges of the picture spreading horizontally.

SMPTE time code

  A signal specified by the Society of Motion Picture and Television Engineers for facilitating videotape editing; this signal uniquely identifies each frame of the video signal. Program originators use vertical blanking interval lines 12 through 14 to store a code identifying program material, time, frame number, and other production information.

SMP

  See standby monitor present frame.

SMT

  See station management.

SNA

  See Systems Network Architecture.

soft guarantee

  A type of guaranteed rate that XFS may fail to meet in order to retry device errors. See also guaranteed rate.

software option

  A software product from SGI, other than the standard system software that comes on your system disk.

source

  In the context of the Video Library, a provider of video input signals.

source address (SA)

  The address of the entity that is the sender of the data. The format for the address is different for each protocol. A single node has different addresses for its different layers (such as data link layer addresses versus network layer ones). Examples are FDDI and 802.5 use 16-bit or 48-bit addresses; Ethernet uses 48-bit addresses; HIPPI uses 24-bit addresses; IP uses 32-bit addresses.

source routing

  A method of routing whereby the originator (sender) dictates the complete route that must be followed by the message in order to reach its destination. Each router/gateway along the route honors the route specified by the sender instead of following any of its usual or known routes. Some types of source routing (for example, Token Ring) are handled by the medium access control sublayer. Other types (for example, IP) are managed by the network layer. For a different routing method, see transparent routing. See also routing.

spool

  A generic term for a directory or program that holds and meters jobs or data for future use. A spool directory is typically a temporary holding place for data that is bound for another place. For example, the printing command `lp`(1) uses spooling to dispatch each print job when the previous one is complete.

spraying interrupts

  In order to equalize workload across all CPUs, the Challenge/Silicon Graphics Onyx systems direct each I/O interrupt to a different CPU chosen at random. In order to protect a real-time program from unpredictable interrupts, you can isolate specified CPUs from sprayed interrupts, or you can assign interrupts to specified CPUs.

stable ring

  A ring condition where no stations are being added or removed. When a ring is stable, the upstream neighbor addresses (UNAs) that stations receive in circulating frames match the UNAs that are stored in their memories.

stacking

  For 802.5 Token Ring, an act whereby a station raises the ring's priority level by generating a token whose priority field contains a value that is higher than the value that was in the captured token.

standalone shell (SASH)

  The SASH is a minimum-functionality operating system that allows you to access files and install software. Typically, the SASH is used to install the IRIX operating system.

standalone workstation

  A workstation that is not connected to a network.

standby monitor

  For 802.5 Token Ring, a monitor that watches the ring to verify that one active monitor exists and that there is no break in the ring. If an active monitor does not exist, standby monitors take action to remedy the problem by token claiming. If a break in the ring occurs, standby monitors starting beaconing. All of the stations on the ring, except one, are standby monitors.

standby monitor present frame (SMP)

  For 802.5 Token Ring, a MAC frame (management frame) generated by each station whose monitor is in the standby monitor state. This frame is used to communicate the upstream neighbor address (UNA), which is essential for monitoring and maintaining ring integrity.

static electricity

  The electrical discharge resulting from the accumulation of electric charge on an insulated body. When your body touches metal parts (including printed circuit boards) of computer equipment, there is the potential for you to feel an electrical shock (electrostatic discharge, or ESD) which could damage the equipment. To prevent this, always wear a wrist strap when working with internal parts of a workstation.

station

  For Token Ring networks (including 802.5 Token Ring and FDDI), a node with a unique MAC (physical layer) address and a network layer address (for example, an IP address or an LU address). Each station is attached to the ring through an adapter.

station management (SMT)

  One of the FDDI standards. The entity within a station that monitors station activity, exercises overall control of station activity, and manages the FDDI ring. The SMT module controls and manages the station's processes at the various FDDI layers. It also works cooperatively with other SMT modules to manage the ring. SMT provides services such as fault isolation and recovery for the ring, maintenance of the local station's MIB, control over station insertion and removal from the ring, and configuration management.

station ID

  An 8-byte (64-bit), site-configurable number used by SMT modules to identify and reference FDDI stations. This number is used only for reporting status information. The FDDIXPress SMT daemon, by default, creates the station ID from the station's MAC address. The six bytes of the MAC address (in canonical order) occupy the lower six bytes of the station ID and the upper two bytes are set to zero.

status information frame (SIF)

  Status information frames are used to request and provide, in response, a station's configuration and operating information in a Token Ring local area network.

stipple

  A one- or two-dimensional binary pattern that defeats the generation of fragments where its value is zero. Line stipples are one-dimensional and are applied relative to the start of a line. Polygon stipples are two-dimensional and are applied with a fixed orientation to the window.

straight-tip (ST) connector

  An optical fiber connector used to join single fibers together.

strip

  For Token Ring networks (including 802.5 Token Ring and FDDI), to remove a data frame from the ring. Each station is responsible for stripping the data frames that it transmits.

striped volume

  A logical disk volume comprising multiple disk drives, in which segments of data that are logically in sequence (“stripes”) are physically located on each drive in turn. As many processes as there are drives in the volume can read concurrently at the maximum rate.

striping

  The method of minimizing disk access time when creating logical volumes. On a striped volume, the workstation lays out the filesystem in stripes and allocates information alternately between the stripes. The principle at work is that the seek time for the disks is shorter because successive read and write operations will take place on different stripes and a different head will be used for each read or write operation. See logical volume.

subcarrier

  A portion of a video signal that carries a specific signal, such as color. See also color subcarrier.

subpixel

  A unit derived from a pixel by using a filter for sizing and positioning.

superblock

  The second (512-byte) block of each filesystem. It provides information about the size of the filesystem and a map to the free space on the disk.

superuser

  A user with root (UID 0) privileges. A user may become superuser by logging in as root, by using the `su` command, or by running programs set up to run as root. See also system administrator.

S-VHS, S-Video

  Video format in which the Y (luminance) and C (chrominance) portions of the signal are kept separate. Also known as YC.

swap space

  When a workstation is running many programs at once, it might run short of available memory. When this happens, sections of program that are not immediately being executed are written out to a special area of the disk, where they can be easily retrieved. That area of disk is known as “swap space” and the action of moving pages of program in and out is known as “swapping” or “paging.”

symbol

  The smallest signaling element used by the data link layer. The FDDI symbol set consists of 16 data symbols and 8 control symbols. Each symbol corresponds to a specific sequence of 5 bits transmitted by the physical layer on the optic cable that is seen by software as a 4-bit sequence. (4-bit to 5-bit conversion, and vice-versa, is done by hardware.)

symbolic link

  When a new filename is linked to an existing file with the `ln -s` command, the link generated is “symbolic.” Symbolic links can exist across filesystem boundaries. The drawback to symbolic links is that not all programs can follow the link back to the original file, as with a “hard link.” See hard link.

sync information

  The part of the television video signal that ensures that the display scanning is synchronized with the broadcast scanning. See also video waveform.

sync pulse

  A vertical or horizontal pulse (or both) that determines the display timing of a video signal. Composite sync has both horizontal and vertical sync pulses, as well as equalization pulses. The equalization pulses are part of the interlacing process.

sync tip

  The lowest part of the horizontal blanking interval, used for synchronization. See also video waveform.

system

  Software and hardware operating together as a functional unit. This can be any of three possible configurations: a standalone personal system (workstation and software); a personal system connected to a larger network; or the larger network itself, consisting of interconnected hardware and software

system administration

  The tasks associated with setting up, maintaining, and troubleshooting a networked or standalone system.

system administrator

  The person responsible for setting up, maintaining, and troubleshooting a system. The system administrator uses the root login account to perform most administrative tasks. See superuser.

system crash

  When the IRIX operating system fails and the system does not accept keyboard or mouse input.

system disk

  The physical disk that contains the standard IRIX operating system software—the software that makes your workstation run.

System Manager

  A set of tools used by the system administrator to set up and manage a system. You access the System Manager through the System toolchest.

system password

  See dialup password.

system software

  The standard IRIX operating system software and SGI tools that come on the system disk and on the tape or CD-ROM that you use in the event of a system crash.

System toolchest

  The toolchest in the upper left-hand corner of the screen labeled System. You can start system tools such as IRIS WorkSpace and System Manager using its menu.

Systems Network Architecture (SNA)

  A family of protocols developed by IBM that make it possible for SNA-speaking computer systems to exchange data and interoperate. SNA has seven layers; each layer handles a specific set of communication functions and provides these services to the adjacent layers. The services defined for each SNA layer do not correspond necessarily to those in the OSI layer at the same relative position.

target token rotation time (TTRT)

  The amount of time a station bids in the Token Ring claim process. The station whose claim indicates that it has the lowest TTRT wins the claim process. This TTRT value is then used by all stations on the network for setting TTRT.

TCP/IP

  The standard networking software included in the system software.

template

  A one-page file that gets inserted on each new page you add. Templates help regulate the format of your documents.

terminal

  A display and keyboard, or a printer and keyboard, for entering programs and data to a computer and for receiving output from a computer

terminal options

  Selectable settings that define the way a terminal operates.

termination

  To send a signal through a transmission line accurately, there must be an impedance at the end that matches the impedance of the source and of the line itself. Amplitude errors, frequency response, and pulse distortions and reflections (ghosting) occur on a line without proper termination. Video is a 75 Ohm system; therefore a 75 Ohm terminator of .5% to .25% accuracy must be installed at the end of the signal path.

tessellation

  Reduction of a portion of an analytic surface to a mesh of polygons, or of a portion of an analytic curve to a sequence of lines.

texel

  A texture element. A texel is obtained from texture memory and represents the color of the texture to be applied to a corresponding fragment.

Text object (in IRIS Showcase)

  A Text object is a block of text you create using one of IRIS Showcase's text tools.

texture

  A one- or two-dimensional image that's used to modify the color of fragments produced by rasterization.

texture mapping

  The process of applying an image (the texture) to a primitive. Texture mapping is often used to add realism to a scene. As an example, you could apply a picture of a building facade to a polygon representing a wall.

texture matrix

  The 4×4 matrix that transforms texture coordinates from the coordinates that they're specified in to the coordinates that are used for interpolation and texture lookup.

texturing

  Applying images to 3D objects to give additional realism to displayed renderings.

threshold

  In a digital circuit, the signal level that is specified as the division point between levels used to represent different digital values. For example, the sync threshold is the level at which the leading edge of sync begins. See also video waveform.

time-base errors

  Analog artifacts caused by nonuniform motion of videotape or of the tape head drum. Time-base errors usually cause horizontal display problems, such as horizontal jitter.

time code

  See SMPTE time code.

time-delay equalization

  Frame-by-frame alignment of all video inputs to one sync pulse, so that all frames start at the same time. This alignment is necessary because cable length differences cause unequal delays. See time-base errors.

token

  For Token Ring networks (including 802.5 Token Ring and FDDI), a control signal (frame) that consists of a unique signaling sequence (pattern) that gives a station the right to transmit on a shared medium (that is, the ring). At any point in time, a ring can have zero or one token circulating, but no more. The token is captured (not repeated onto the ring) by a station that wants to transmit data. At any point in time, the token may be held by zero or one station. The token is regenerated (put back onto the ring) when the transmitting station finishes transmitting.

token claiming

  A ring management process whose goal is to make one station into the active monitor for the ring. The absence of an active monitor causes token claiming to start. During the token claiming process, one or more stations transmit claim token frames. All stations refrain from transmitting data during token claiming. When a token claiming station sees its own claim token frame return, and when that frame's upstream neighbor address (UNA) matches the station's previously received (stored) UNA value, the station becomes the active monitor. The event that causes a station to start token claiming is failure to see an active monitor present or token frame for a period of time. (The length of this time period is defined by the 802.5 Token Ring Standard.)

token holding timer

  A timer that controls the maximum amount of time a station can use (occupy) the transmission medium (cable). The transmission medium is “occupied” as long as the station holds the token. When this timer expires, the station must place the token back onto the ring. The length for this timer is defined by the 802.5 Token Ring Standard.

token ring

  A set of stations serially connected by a transmission medium (cable) to form a closed loop.

token rotation time (TRT)

  The maximum time that a token needs to make a complete circuit around the ring.

Toolchest window

  The window that contains the five toolchests. It appears in the upper left corner of the screen.

trace

  A Token Ring RMT function that attempts to provide ring recovery when there is a stuck (continuous) beacon condition on the ring. The trace causes all stations and concentrators upstream from the tracing SMT to leave the ring and perform a Path Test. When the stuck device is isolated, the ring is wrapped so as to exclude the stuck device.

transcoder

  A device that converts a component video signal to a different component video signal, for example, RGB to Y/R-Y/B-Y, or D1 to RGB.

transducer

  A microphone, video camera, or other device that can convert sounds or images to electrical signals.

transformation (in OpenGL)

  A warping of space. In OpenGL, transformations are limited to projective transformations that include anything that can be represented by a 4×4 matrix. Such transformations include rotations, translations, (nonuniform) scalings along the coordinate axes, perspective transformations, and combinations of these.

translation lookaside buffer (TLB)

  An on-chip cache of recently used virtual-memory page addresses, with their physical-memory translations. The CPU uses the TLB to translate virtual addresses to physical ones at high speed. When the IRIX kernel alters the in-memory page translation tables, it broadcasts an interrupt to all CPUs, telling them to purge their TLBs.

transmit

  The action of a station generating a frame, token, or control sequence and placing it on the medium to the next station.

transmitter (optical)

  An opto-electronic circuit that converts an electrical logic signal to an optical signal.

transparent routing

  Also called, hop-by-hop routing. A method of routing whereby the originator (sender) of a packet/datagram specifies only the destination address, and a router/gateway on the sender's LAN does the routing to either the destination system or to the next stop along the way to the destination. The sender does not specify, and does not need to know, the complete route. Each router (intermediate system) that receives the packet looks at the destination address, decides which of its known routes is best for reaching the destination, and sends the packet to the next step along that route, until the destination is reached.

transport delay

  The time it takes for a simulator to reflect a control input in its output display. Too long a transport delay makes the simulation inaccurate or unpleasant to use.

tree

  A physical topology consisting of a hierarchy of master-slave connections between a concentrator and other FDDI nodes (including subordinate concentrators)

triangle

  A polygon with three edges. Triangles are always convex.

tristimulus color system

  A system of transmitting and reproducing images that uses three color signals, for example, RGB, YIQ, and YUV.

TRT

  See token rotation time.

trunk

  For token ring networks (including 802.5 Token Ring and FDDI), an adjective specifying that something is attached to the main ring (as opposed to an entity indirectly attached to the ring through a concentrator). For FDDI, the trunk ring consists of two optical fibers with counter-rotating signals).

trunk coupling unit (TCU)

  For 802.5 Token Ring, a hardware device that enables one or more stations to connect to the trunk cable. The TCU can insert the station onto the ring as well as bypass the connection to a station that is missing or dysfunctional. Examples of TCUs include multistation access units, lobe attachment modules, and other concentrators.

TTRT

  See target token rotation time.

TTY

  An abbreviation for teletypewriter, the term covers the area of access between the IRIX system and peripheral devices, including the system console.

TTY line

  The physical wire through which access to the computer is made. See port.

U signal

  One of the chrominance signals of the PAL color television system, along with V. Sometimes referred to as B-Y, but U becomes B-Y only after a weighting factor of 0.493 is applied. The weighting is required to reduce peak modulation in the composite signal.

U-Matic

  Sony trademark of its 3/4-inch composite videotape format. SP U-Matic is an improved version using metal tape.

underrun exception

  When a process scheduled by the Frame Scheduler should have started in a given minor frame but did not (owing to being blocked), an underrun exception is signaled. See also overrun exception.

underscan

  To scan a television screen so that the edges of the raster are visible. See also overscan.

UNIX

  A multiuser, multi-tasking operating system from AT&T on which the SGI IRIX operating system is based.

unmount

  To make a filesystem that is accessible from a specific directory on your workstation temporarily inaccessible. See mount.

upgrade

  Hardware that you add to the basic system that increases performance, such as additional memory (SIMMs) or faster graphics boards.

upstream

  An adjective denoting the relative position for an entity, indicating that it resides in the direction from where the main signal comes. An upstream component is closer to the source of the signal than the entity of reference. For example, on a Token Ring network, upstream stations are those that see and repeat the signal before the station in question.

upstream neighbor address (UNA)

  For Token Ring networks (including 802.5 Token Ring and FDDI), the physical address (MAC address) of the station that transmits/repeats immediately before the station in question. The upstream neighbor's address (UNA) is one of the most important items for monitoring the health of a ring because a station can become aware of instability in the ring only as a change in its upstream neighbor or as the failure to receive a signal from the upstream neighbor. Because of this, each station on a token ring must keep track of its UNA. As long as a station continues to receive frames indicating the same UNA, the ring is stable. When the UNA in the current frame does not match the previously received (stored) UNA, the ring configuration is changing. For example, the old upstream neighbor may have failed or may have been removed.

user ID (UID)

  A number that uniquely identifies a user to the system.

V signal

  One of the chrominance signals of the PAL color television system, along with U. Sometimes referred to as R-Y, but V becomes R-Y only after a weighting factor of 0.877 is applied. The weighting is required to reduce peak modulation in the composite signal.

vectorscope

  A specialized oscilloscope that demodulates the video signal and presents a display of R-Y versus B-Y for NTSC (V and U for PAL). Video engineers use vectorscopes to measure the amplitude (gain) and phase angle (vector) of the primary (red, green, and blue) and the secondary (yellow, cyan, and magenta) color components of a television signal.

VERSA-Model Eurocard (VME) bus

  A hardware interface and device protocol for attaching I/O devices to a computer. The VME bus is an ANSI standard. Many third-party manufacturers make VME-compatible devices. The Challenge/Silicon Graphics Onyx and Crimson systems support the VME bus.

vertex

  A point in three-dimensional space.

vertical blanking

  The portion of the video signal that is blanked so that the vertical retrace of the beam is not visible.

vertical blanking interval

  The blanking portion at the beginning of each field. It contains the equalizing pulses, the vertical sync pulses, and vertical interval test signals (VITS). Also the period when a scanning process is moving from the lowest horizontal line back to the top horizontal line.

vertices

  Plural of vertex. See indices.

video level

  Video signal amplitude.

video on demand (VOD)

  In general, producing video data at video frame rates. Specific to guaranteed rate, a disk organization that places data across the drives of a striped volume so that multiple processes can achieve the same guaranteed rate while reading sequentially. See also guaranteed rate, striped volume.

video output

  See drain.

video signal

  The signal from a video device, such as a camera, VCR, or other scanning image sensor.

video waveform

  The main components of the video waveform are the active video portion and the horizontal blanking portion. Certain video waveforms carry information during the horizontal blanking interval.

viewpoint

  The origin of either the eye- or the clip-coordinate system, depending on context. (For example, when discussing lighting, the viewpoint is the origin of the eye-coordinate system. When discussing projection, the viewpoint is the origin of the clip-coordinate system.) With a typical projection matrix, the eye-coordinate and clip-coordinate origins are at the same location.

view volume

  The volume in clip coordinates whose coordinates satisfy the three conditions:

  -w ≤ x ≤ w

  -w ≤ y ≤ w

  -w ≤ x ≤ w

  Geometric primitives that extend outside this volume are clipped.

virtual size

  The aggregate size of all the pages that are defined in the address space of a process. The virtual size of a process is reported by `ps`(1) under the heading SZ. The sum of all virtual sizes cannot exceed the size of the swap space. See also resident set size.

virtual address space

  The set of numbers that a process can validly use as memory addresses.

white level

  In the active video portion of the video waveform, the 1.0-volt (100 IRE) level. See also video waveform.

wildcard

  A character, usually an asterisk (*), that you use alone to specify all files and directories that are available, or with a few other letters to specify a group of files and directories that have a common element in their names. For example, to specify all files and directories that begin with the letters “ch”, you would type: `ch*`

window (in OpenGL)

  A subregion of the framebuffer, usually rectangular, whose pixels all have the same buffer configuration. An OpenGL context renders to a single window at a time.

window

  A portion of the screen that you can manipulate that contains text or graphics.

window-aligned

  When referring to line segments or polygon edges, window-aligned implies that these are parallel to the window boundaries. (In OpenGL, the window is rectangular, with horizontal and vertical edges). When referring to a polygon pattern, window-aligned implies that the pattern is fixed relative to the window origin.

window coordinates

  The coordinate system of a window. It's important to distinguish between the names of pixels, which are discrete, and the window-coordinate system, which is continuous. For example, the pixel at the lower left corner of a window is pixel (0, 0); the window coordinates of the center of this pixel are (0.5, 0.5, z). Note that window coordinates include a depth, or z, component, and that this component is continuous as well.

window manager

  The system program that draws and controls windows. It lets you create and manipulate windows — move them, resize them, and close them.

wireframe

  A representation of an object that contains line segments only. Typically, the line segments indicate polygon edges.

wiring concentrator (WC)

  See concentrator.

WorkSpace window

  The main window for working with icons and customizing your view of the filesystem. You place files and directories from all over the filesystem here for easy access; placing them in the WorkSpace does not change their actual location in the filesystem.

workstation

  The hardware, which can include graphics boards, CPU(s), system disk, power supply, chassis, cover, monitor, keyboard, mouse, and other peripherals. These elements are connected and function together so that a user can work. A workstation may operate independently or may be connected to a larger network (or both).

wrap

  A condition in which the primary ring of an FDDI local area network loops to (is connected to) the secondary ring. Wraps occur when there is a fault on the primary ring. The fault or break in the primary ring prevents the optical signal from completing the loop around the ring, thus stopping all communication. Wrapping reestablishes the loop and allows communication to continue. When a ring is wrapped, one or more ports have been left out of the ring.

X Window System

  A window system used by many of the systems on which OpenGL is implemented. GLX is the name of the OpenGL extension to the X Window System.

xon-xoff

  A protocol that uses a combination of hardware and software signals to control the flow of information between a workstation and a printer. It is also referred to as a software handshake.

Y signal

  Luminance, corresponding to the brightness of an image. See also luminance, Y/R-Y/B-Y.

YC

  A color space (color component encoding format) based on YIQ or YUV. Y is luminance, and the two chroma signals (I and Q or U and V) are combined into a composite chroma called C, resulting in a two-wire signal. C is derived from I and Q as follows:

  C - I cos(2Ľfsct) + Q sin(2Ľfsct)

  where fsc is the subcarrier frequency. YC-358 is the NTSC version of this luminance/chrominance format; YC-443 is the PAL version. Both are referred to as S-Video formats.

YIQ

  A color space (color component encoding format) used in decoding, in which Y is the luminance signal and I and Q are the chrominance signals. The two chrominance signals I and Q (in-phase and quadrature, respectively) are two-phase amplitude-modulated. The I component modulates the subcarrier at an angle of 0 degrees, and the Q component modulates it at 90 degrees. The color burst is at 33 degrees relative to the Q signal.

  The amplitude of the color subcarrier represents the saturation values of the image; the phase of the color subcarrier represents the hue value of the image.

  Y = 0.299R + 0.587G + 0.114B

  I = 0.596R - 0.275G - 0.321B

  Q = 0.212R - 0.523G + 0.311B

Y/R-Y/B-Y

  A name for the YUV color component encoding format that summarizes how the chrominance components are derived. Y is the luminance signal and R-Y and B-Y are the chrominance signals. R-Y (red minus Y) and B-Y (blue minus Y) are the color differences, or chrominance components. The color difference signals R-Y and B-Y are derived as follows:

  Y = 0.299R + 0.587 + 0.114B

  Y/R-Y/B-Y has many variations, just as NTSC and PAL do. All component and composite color encoding formats are derived from RGB without scan standards being changed. The matrix (amount of red, green, and blue) values and scale (amplitude) factors can differ from one component format to another (YUV, Y/R-Y, B-Y, SMPTE Y/R-Y, B-Y).

YUV

  A color space (color component encoding format) used by the PAL video standard, in which Y is the luminance signal and U and V are the chrominance signals. The two chrominance signals U and V are two-phase amplitude-modulated. The U component modulates the subcarrier at an angle of 0 degree, but the V component modulates it at 90 degrees or 180 degrees on alternate lines. The color burst is also line-alternated at +135 and -135 degrees relative to the U signal. The YUV matrix multiplier derives colors from RGB via the following formula:

  Y = .299R + .587 G + .114 B

  CR = R - Y

  CB = B - Y

  In this formula, Y represents luminance; red and blue are derived from it: CR denotes red and (V), CB denotes blue. V corresponds to CR; U corresponds to CB c. The U and V signals are carried on the same bandwidth. This system is sometimes referred to as Y/R-Y/B-Y.

  Note: The name for this color encoding method is YUV, despite the fact that the order of the signals according to the formula is YVU.

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