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back margin. The margin of a page that is closest to the binding edge. Normally, this is the left margin of the recto page and the right margin of the verso page.

back up. To copy information, usually onto diskette or tape, for safekeeping.

backdrop. In CDE, the pattern that covers the workspace background.

backend. The program that sends output to a particular device. There are two types of backends: friendly and unfriendly.

backend program. See backend.

backfacing polygon. In GL, a polygon whose vertices appear in clockwise order in screen space. If backface culling is enabled, such polygons are not drawn.

background. (1.) In multiprogramming, the conditions under which low-priority, noninteractive programs are run. Contrast with foreground. See also program level. (2.) In CDE, the underlying area of a window on which elements, such as buttons and lists, are displayed.

background activity. See background process.

background color. In AIXwindows and Enhanced X-Windows, the single electronic color assigned to the graphic field that appears behind the foreground elements inside the border of a displayed widget or gadget. Contrast with foreground color.

background process. (1.) A process that does not require operator intervention but can be run by the computer while the workstation is used to do other work. (2.) A mode of program execution in which the shell does not wait for program completion before prompting the user for another command. Contrast with foreground process.

backing store. The collection of off-screen, saved pixels maintained by the Enhanced X-Windows server.

backscrolling. (1.) Reversing the normal (top-to-bottom) direction of flow of paper through a printer. (2.) In reference to a video display, moving text through the viewing area from top to bottom.

Backtrack. In CDE, in Help Manager, a button and Navigate menu item you use to follow links backward, in the reverse order they were traversed.

backup. Pertaining to a system, device, file, or facility that can be used in the event of a malfunction or loss of data.

backup copy. A copy, usually of a file or group of files, that is kept in case the original file or files are unintentionally changed or destroyed.

backup format. When the backup command makes a copy of a file, it writes the file in this format. A file in this format must be restored by the restore command before it can be used.

backup format file. A file in backup format.

backup system. See dump and restore.

bad block. A portion of a disk that can never be used reliably.

bandwidth. Data rate transfer in K bits, K bytes, M bits, and M bytes per second.

base address. The beginning address for resolving symbolic references to locations in storage.

base address register. Synonym for base register.

base class. A C++ class from which other classes are derived. A base class may itself be derived from another base class.

base line. See baseline.

base name. (1.) The last element to the right of a full path name. (2.) A file name specified without its parent directories. (3.) In Ada language, a compilation unit name specified without its type qualifier of lib/ or sec/. (4.) In CDE, The file name of an icon file minus the file-name suffixes for size (.l, .m, .s, .t) and type (.bm, .pm). For example, the base name of an icon file named myicon.m.pm is myicon.

base number. The part of a self-check field from which the check digit is calculated.

Base Operating System (BOS) installation. The process of installing and configuring the minimum amount of software needed to bring a machine to the running state.

base permission. An access mode that is assigned to a file owner, file group, or others who want access to the file. Access modes include read (r) permission, write (w) permission, and execute/search (x) permission. See also discretionary access control.

base register. A general purpose register that the programmer chooses to contain a base address. Synonym for base address register. See also index.

base scalar type. In Pascal, the type from which a set type or subrange type is derived. See also subrange scalar type.

baseband system. A communications system whereby information is encoded, modulated, and impressed on the transmission medium without shifting or altering the frequency of the information signal. At any point on the medium, only one information signal at a time is present.

baseline. In a font, the imaginary line on which the bottom of each character is aligned.

BASIC (beginner's all-purpose symbolic instruction code). (1.) A programming language designed for interactive systems. Originally developed at Dartmouth College to encourage people to use computers for simple problem-solving operations. (2.) A high-level programming language with a small number of statements and a simple syntax. BASIC is designed to be easily learned and used and is widely used for interactive applications on microcomputers.

basic conversation. A connection between two transaction programs that allows them to exchange logical records that contain a 2-byte prefix that specifies the length of the record. LUs 1, 2, and 3 do not use the 2-byte prefix; however, LU 1, 2, and 3 conversations must be basic conversations. This conversation type is used by service transactions and LU 1, 2, and 3 application transaction programs. Contrast with mapped conversation.

Basic Encoding Rules (BER). A set of rules used to encode ASN.1 values as strings of octets.

basic increment. The smallest unit of motion of which a device is capable.

Basic Input/Output System. See BIOS.

Basic Networking Utilities (BNU). A group of programs and files, sometimes called the UNIX-to-UNIX Copy Program, that provides basic networking utilities, such as the uucp command. BNU includes a set of directories, files, programs, and commands that allow the user to communicate with a remote UNIX system over a dedicated line or a telephone line. See also UNIX-to-UNIX Copy Program and UUCP login ID.

basic real constant. A string of decimal digits containing a decimal point and expressing a real value.

basis. In GL, a curve or patch basis is a 4x4 matrix that controls the relationship between control points and the approximating spline. B-splines, Bezier curves, and Cardinal splines all differ in that they have different bases.

batch printing. Queueing one or more documents to print in a separate job as a background process. The operator can type or revise additional documents at the same time. This is a background process. See also background process.

batch processing. A processing method in which one or more programs process records with little or no operator action. This is a background process. Contrast with interactive processing.

battery backup. A power source that allows the processor drawer and other data storage devices to continue operating during a primary AC power source outage.

baud. (1.) The number of changes in signal levels, frequency, or phase per second on a communication channel. If each baud represents 1 bit of data, baud is the same as bits per second. Informally (as used by programmers) synonymous with "bits per second." Named for J. Baudot, 1845-1903, French inventor. However, it is possible for one signal change (1 baud) to equal more than 1 bit of data. (2.) A unit of signaling speed equal to the number of discrete conditions or signal events per second. For example, 1 baud equals one-half dot cycle per second in Morse code, 1 bit per second in a train of binary signals, and one 3-bit value per second in a train of signals that can each assume one of eight different states. (3.) In asynchronous transmission, the unit of modulation rate corresponding to one unit interval per second; for example, if the duration of the unit interval is 20 milliseconds, the modulation rate is 50 baud. See also bps.

baud rate. In remote communications, the transmission rate that is synonymous with signal events. The baud rate is usually expressed in bits per second.

BCUG. See bilateral closed user group.

behavior (of an object). In SOM, the methods that an object responds to. These methods are those either introduced or inherited by the class of the object. See also state.

BEL. The bell character. A control character that activates an alarm or other attention devices when human attention is required. Synonym for console bell.

benchmark. A program designed to test the relative performance of computers of different architectures, or of different implementations of an architecture. The combination of a rigorously specified workload and a method of quantifying the performance of a system when processing that workload. The performance metric is usually derived from the time required to process the workload.

BER. See Basic Encoding Rules.

Bezier cubic curve. In GL, a cubic spline approximation to a set of four control points that passes through the first and fourth control points, and has a continuous slope where two spline segments meet. See also parametric cubic curve.

BGP. Border Gateway Protocol.

bibliography. A list of documents referred to within a document. For each document, the following is generally listed: the author, the document, notes about the document, and sometimes notes about its author.

bid. In the contention form of invitation or selection, an attempt to gain control of a line to transmit data.

bidirectional. See shared port.

big endian. An attribute of data representation that reflects how multi-octet data are stored in memory. In big endian representation, the lowest addressed octet of a multi-octet data item is the most significant. See also endian and little endian.

big endian order. The method of storage in which integer values are stored most significant byte first. See also little endian order.

big word. In the vi editor, a contiguous set of alphanumeric characters bounded at the beginning and end by blank spaces, tabs, or new-line indicators. See also small word.

bilateral closed user group (BCUG). In X.25 communications, an optional facility that allows calls to be made only between two designated DTEs. See also closed user group.

bin collection. A method of collecting auditing data that writes audit records to a temporary bin file. After the data is processed by the auditbin daemon, records are written to an audit trail file for storage.

binary. (1.) Pertaining to a system of numbers to the base two. The binary digits are 0 and 1. (2.) Involving a choice of two conditions, such as on-off or yes-no. (3.) In ODM, a terminal descriptor type used to define a variable as a bit string that is not null-terminated. See also terminal descriptor.

binary constant. A constant that is made up of one or more binary digits.

binary digit. Synonym for bit.

binary expression. An expression containing two operands and one operator.

binary file. A file that contains codes that are not part of the ASCII character set. Binary files can utilize all 256 possible values for each byte in the file.

binary-image transfer. See bit block transfer.

binary operator. (1.) A symbol representing an operation to be performed on two data items, arrays, or expressions. The four types of binary operators are numeric, character, logical, and relational. Contrast with unary operator. (2.) An arithmetic operator that has two terms. Synonym for dyadic operator.

binary search tree. A search structure in which, at each step of the search, the set of data elements is divided by two; some appropriate action is taken in the case of an odd number of data elements.

binary synchronous communication (BSC). A form of telecommunication line control that uses a standard set of transmission control characters and control character sequences for binary synchronous transmission of binary-coded data between stations. Contrast with synchronous data link control.

bind. (1.) To associate a variable with an absolute address, identifier, or virtual address, or with a symbolic address or label in a program. (2.) In SNA, a request to activate a session between two logical units. See also bind session. (3.) For information on how to set a binding, see also set.

BIND. See bind session.

bind image. In SNA, the session parameters that the system services control point (SSCP) sends to the primary logical unit (PLU) and the PLU sends in the BIND request to the secondary logical unit (SLU); these parameters specify the proposed protocol options for an LU-LU session.

BIND password. One of the two communication security passwords. In an LU-LU session, it is the password that the system checks against the remote system to verify that the program to which the user is connected is the correct one. See also node verification and communications authority password.

bind session (BIND). In SNA products, a request to activate a session between two logical units. See also bind.

binder. See linkage editor.

binding. (1.) A temporary association between a client and both an object and a server that exports an interface to the object. A binding is meaningful only to the program that sets it and is represented by a bound handle. (2.) In SOM, Language-specific macro or procedure that makes implementing and using SOM classes more convenient. These bindings offer a convenient interface to SOM that is tailored to a particular programming language. The SOM Compiler generates binding files for C and C++. These binding files include an implementation template for the class and two header files, one to be included in the class's implementation file and the other in client programs. (3.) In a multiprocessor context, constraining a thread to a specific physical processor to gain the benefit of processor affinity.

binding edge. The edge of a page, perforated for loose binding, to be bound, stapled, or drilled.

BIOS (Basic Input/Output System). In the Personal Computer AT, microcode that controls basic hardware operations such as interactions with diskette drives, fixed-disk drives, and the keyboard.

bis . Describes a secondary recommendation that is an alternative to a primary recommendation.

BIST. Built-in self-test.

bit. Either of the binary digits 0 or 1 used in computers to store information. Synonymous with binary digit. See also byte.

bit block transfer (BLT). The movement of a binary image (bitmap or pixmap) by specifying the lower-left and upper-right corners of the image and the destination address.

bit BLT. See bit block transfer.

bit clocking. In an EIA-232C or D interface, the field that indicates which piece of equipment, either the modem (DCE) or the computer (DTE), provides the clock signal for synchronized data transactions.

bit field. A member of a structure or union that contains 1 or more named bits.

bit gravity. In Enhanced X-Windows, the attraction of window contents for a location in a window. When a window is resized, its contents can be relocated. The server can be requested to relocate the previous contents to a region of the window. See also gravity.

bit planes. In computer graphics, a bitplane supplies one bit of color information per pixel on the display. Thus, an eight bitplane system allows 2 to the eighth power different colors to be displayed at each pixel.

bit rate. The speed at which bits are transmitted, usually expressed in bits per second.

bit scattering. A technique for mapping memory bits to ensure that a minimum number of bits in a memory word are stored in a single DRAM. With a minimum number of bits, the ECC is better able to detect and correct errors caused by a bad DRAM.

bitmap. A pixmap with a depth of one bit plane.

bitmap file. The file containing the height and width instructions for creating a bitmap.

bitmapped display. A display with a display adapter that has a hardware representation of each separately addressable point on the display. The hardware representation can be processor memory or adapter memory. See also All Points Addressable Display.

bits per character. The number of bits in a data character.

blank common. In FORTRAN, an unnamed common block.

blind folio. A document in which the pages of the document are counted but not numbered. See also folio, dropped folio, and expressed folio.

blit. Bit block transfer.

block. (1) A group of contiguous records recorded or processed as a unit. Blocks are separated by interblock gaps and each block may contain one or more records. (2) In data communications, a group of records that is recorded, processed, or sent as a unit. (3) In programming languages, a compound statement that coincides with the scope of at least one of the declarations contained within it. A block may also specify storage allocation or segment programs for other purposes.

block data subprogram. In FORTRAN, a subprogram headed by a BLOCK DATA statement that is used to initialize variables in named common blocks.

block device. (1.) One of the types of files in the file system, described by an i-node. (2.) A device that is accessed by means of a device driver.

block file. A file listing the usage of blocks on a disk. See also special file and character special file.

block input/output communication area (BIOCA). A block of storage in the kernel address space that is used to communicate with a block I/O subsystem.

block I/O. Input/output operations on blocks of data stored in random locations.

block special file. A special file for a block device. The file provides access to an input or output device that uses in-core buffers and is capable of supporting a file system. See also character special file.

block statement. Any number of data definitions, declarations, and statements that appear between the symbols { (left brace) and } (right brace). The C language, for example, reads a block statement as a single C language statement. In Ada language, a block statement is a single statement that may contain a sequence of statements. It may also include a declarative part, and exception handlers; their effects are local to the block statement. See also statement.

blocking. An optimization that involves changing the access order of loops that access large arrays, so that each array element is accessed as infrequently as possible.

blocking call. A call in which a caller is suspended until a called procedure completes.

blocking factor. The number of iterations of an inner loop that are executed for each pass of a corresponding blocking loop.

BLT. See bit block transfer.

BNC. A connector used with some coaxial cables.

BNU. See Basic Networking Utilities.

BOA (basic object adapter) class. In SOM, a CORBA interface (represented as an abstract class in DSOM), which defines generic object-adapter (OA) methods that a server can use to register itself and its objects with an ORB (object request broker). See also SOMOA (SOM object adapter) class and ORB (object request broker).

body. (1.) On a printed page, the portion of the page that contains the main text, excluding the margins, headers, footers, and footnotes. (2.) In a book, the portion between the front matter and the back matter. (3.) In Ada language, a body defines the execution of a subprogram, package, or task. A body stub is a form of body that indicates that this execution is defined in a separately compiled subunit.

boldface. A heavy-faced type, generally a heavier version of a regular text font. Also, the process of printing in this type. See also double-strike and emphasized.

Boolean. A binary numbering system named after mathematician George Boole in which zero and one are the only two values that can be returned. Traditionally, a value of zero represents FALSE while a value of one represents TRUE. A value of TRUE or FALSE, where TRUE=1 AND FALSE=0.

boot. See initial program load.

boot block. In a file system, the first block where the bootstrap program resides. See also bootstrap block.

boot device. The device that assigns the fixed disk within the root volume group (rootvg) that will contain the startup (boot) image.

boot image. An image containing the kernel, file systems, libraries, and programs. The boot image is loaded after the machine is turned on or reset and brings it to a running state.

boot processing. The type of processing that occurs when a boot image is loaded. The type of boot device (disk, tape, or network) determines the type of boot processing that occurs. Boot processing over the network brings a machine to the running state, the BOS installing state, or the diagnostic state depending on the configuration file.

bootstrap. A small program that loads larger programs during system initialization.

bootstrap block. Synonym for boot block.

border. A visual boundary that separates a displayed object from everything else on a screen.

BOS (Base Operating System). The collection of programs that controls the resources and the operations of the computer system.

bosinst.data. The file that controls the actions of the BOS installation program.

bottleneck. An area of code within a program that uses CPU resources inefficiently and therefore causes unnecessary delays.

bottom shadow. In AIXwindows, a narrow band of a dark color across the bottom of a rectangular graphical object (a widget or gadget) that creates a three-dimensional appearance when the object is manipulated.

boundary alignment. The position in main storage of a fixed-length field, such as halfword or doubleword, on an integral boundary for that unit of information. For example, a word boundary is a storage address evenly divisible by four.

bounding box. (1.) In computer graphics, the bounding box of a character is the smallest rectangle that encloses the shape at the x, y origin. (2.) In GL, a two-dimensional rectangle that bounds a primitive. A bounding box can be used to determine whether the primitive lies inside a clipping region. See also character cell and clipping.

bounds violation. An attempt to access an array using an index or pointer that references storage outside of the array.

box. A line enclosure around text or a table.

bpi. Bits per inch, a measure of linear density for storage products.

bps. Bits per second. In serial transmission, the instantaneous bit speed with which a device or channel transmits a character. See also baud.

braces. (1.) The characters { (left brace) and } (right brace), also known as "curly brackets." These ASCII characters are primary symbols in the C programming language in which the operating system is written. (2.) In Pascal, comment delimiters.

bracket read lock. A shared lock that is obtained, held only for the duration of the current operation, and then immediately dropped. This lock mode ensures that only committed data is read. It does not guarantee that successive reads of the data will yield the same value, because other transactions can immediately modify the value after the read operation is complete and the lock is dropped.

brackets. (1.) The ASCII characters [ (left bracket) and ] (right bracket), also known as "square brackets." (This usage does not follow the British usage of "brackets" to mean parentheses, the characters that enclose this sentence.) (2.) In SNA, one or more chains of request units and their responses, which are exchanged between two LU-LU half-sessions and represent a transaction between them. A bracket must be completed before another bracket can be started. Examples of brackets are database inquiries and replies, update transactions, and remote-job-entry output sequences to workstations.

branch. In a computer program, an instruction that selects one of a number of alternative sets of instructions. A conditional branch occurs only when a specified condition is met. An instruction that selects one of a number of alternative sets of instructions.

branch processing unit. A processing unit that processes branch instructions and dispatches fixed- and floating-point instructions to the fixed-point unit and floating-point unit.

break condition. In the TTY subsystem, a character framing error in which the data is all zeros.

break signal. A signal sent over a remote connection to interrupt current activity on the remote system.

break statement. A C language control statement that contains the keyword break and a semicolon.

break value. In allocating data segment space, the address of the first location beyond the current end of the data segment.

breakpoint. A place in a computer program, usually specified by an instruction, where execution may be interrupted by external intervention or by a monitor program.

bridge. (1.) In the connection of local loops, channels, or rings, the equipment and techniques used to match circuits and facilitate accurate data transmission. (2.) A functional unit that connects two local area networks (LANs) that use the same logical link control (LLC) procedure but may use different medium access control (MAC) procedures. Contrast with gateway.

broadband. Transmission media and techniques that use a broad frequency range, divided into sub-bands of narrower frequency, so that different kinds of transmission can occur at the same time.

broadband channel. A data transmission channel 6 MHz wide. Synonym for wide band channel.

broadcast. Simultaneous transmission of data to more than one destination.

broadcast topology. The topology in which all stations are connected in parallel with the medium and are capable of concurrently receiving a signal transmitted by any other station connected to the medium.

broken pipe message. A message that occurs if the pipe becomes unsynchronized.

broker. In NCS, a server that manages information about objects and interfaces to the objects. A program that wishes to become the client of an interface can use a broker to obtain information about servers that export the interface. See also Location Broker.

browse. (1.) A function available when you select the List of Books button at the bottom of a navigation window. You can move forward and backward through an online book in the same way you can move through a book in hardcopy. (2.) In the xtalk and xroute commands, to view the details of an entry in the routing list or address list.

BSC. See Binary Synchronous Communication.

BSD. Berkeley Software Distribution.

B-spline cubic curve. In computer graphics, a cubic spline approximation to a set of four control points having the property that slope and curvature are continuous across sets of control points. See also parametric cubic curve.

BTU. (1.) British thermal unit. (2.) In SNA, basic transmission unit.

bucket. One or more fields that accumulate the result of an operation.

bucket counts. The number of elements greater than or equal to the lowest limit and less than or equal to the higher limit.

buffer. (1.) A temporary storage unit, especially one that accepts information at one rate and delivers it at another rate. (2.) An adjustable memory storage space, temporarily reserved for performing input or output, into which data is read or from which data is written.

buffer length. The maximum length of a data segment that can be stored in a given buffer.

bug. An error in a program or a logic problem in the intent of the program.

BUID. See bus unit identification.

build code. The program that runs the build process to convert source files into a hypertext database. The build code defines which items can be built into hypertext and which cannot. For example, an illegal font does not build because it is not included in the build code.

built-in function. A function known to the compiler, whose code is incorporated directly into a program module rather than referenced through a library call.

bulletin board. A graphic object that simulates a real-life bulletin board in that it displays text and graphic information in the form of messages to the user from client applications that are currently running.

bundle. A collection of software products available for installation.

burst pages. On continuous-form paper, pages of output that can be separated at the perforations.

bus. (1.) In a processor, a physical facility on which data is transferred to all destinations but from which only addressed destinations can read in accordance with appropriate conventions. (2.) A computer configuration in which processors are interconnected in series. (3.) One or more conductors that transmit signals or power.

bus-in. A unidirectional data bus that is part of the System 360/370 parallel-I/O interface. This bus passes data from the system unit to the host.

Bus Master. A device on the Micro Channel bus that has its own built-in DMA controller instead of using the system-provided DMA controller. This allows the device to set up the DMA transfer itself instead of relying on the system software to set up the system DMA controller, giving the device greater flexibility in function and, in general, better system performance than a DMA slave device. See also DMA slave.

bus-out. A unidirectional data bus that is part of the System 360/370 parallel-I/O interface. This bus passes data from the host to the system unit.

bus unit identification. A field in the I/O Segment register that is decode to select the IOCC for the particular hardware implementation.

busy light. In CDE, a control that blinks when a Front Panel action has been invoked prior to the appearance of a window or when reloading actions.

button. (1.) A word or picture on the screen that can be selected. Once selected and activated, a button begins an action in the same manner that pressing a key on the keyboard can begin an action. (2.) Buttons include those on the keyboard, mouse, lightpen, or buttons on the dial and button box.

button grabbing. Enacting an active grab using a mouse button. See also grab, pointer grabbing, key grabbing, passive grab, and active grab.

button press. The initiation of a function by pressing a mouse button.

byte. (1.) The amount of storage required to represent 1 character; a byte is 8 bits. (2.) A binary character operated on as a unit and usually shorter than one word. (3.) A string that consists of a certain number of bits (usually 8) treated as a unit, and that represents a character. (4.) A group of 8 adjacent binary digits representing 1 EBCDIC character. (5.) In X.25, a byte is called an octet. See also bit.

byte boundary. Memory addressing based on 8-bit intervals. Each memory location contains an 8-bit value that can range from 0 to 255 in decimal notation.

byte constant. In FORTRAN, a named constant that is of type byte.

byte order. In Enhanced X-Windows, the order of bytes as defined by the server for pixmap or bitmap data. Clients with different native byte ordering must swap bytes as necessary.

byte type. In FORTRAN, a binary character operated on as a unit and usually shorter than a computer word.

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