B

background process --
A process that does not require interaction with the user to run. While a background process runs, the user can continue using other programs or commands. Background processing enables the operating system to execute multiple programs or commands at the same time.

background process group --
(programming) Any process group that is not the foreground process group of a session that has established a connection with a controlling terminal.

backquoted expression --
(programming) A command line enclosed in backquotes, whose output is returned as a value. The output of the command replaces the backquotes and the command line within the backquotes.

backup --
A copy of one or more files, directories, or filesystems that is stored apart from the original to safeguard against unplanned deletion. Used as a verb, it means to create a backup copy. See also archive.

badhost/baduser --
An MMDF mail channel through which all e-mail addressed to unrecognized hosts or users is routed. For Sendmail, unrecognized e-mail is sent to a smart host.

banner line --
(programming) The top line of the screen in FMLI applications, used to display the application's title and a Working message that indicates when the application is busy.

bad block --
A sector of a storage medium which cannot store data reliably.

bandwidth --
A measurement of the amount of information that can be passed through a communication channel in a given amount of time. Bandwidth is usually given in units of bits per second.

base level --
(programming) The code that synchronously interacts with a user program. The driver's initialization and switch table entry point routines constitute the base level.

base processor --
The first processor in the system. Also called the default processor, it cannot be deactivated.

bell --
The tone produced by a terminal or computer. The tone is sometimes used to indicate an invalid keystroke, an error, or a finished process.

benchmark --
Software that is run on a computer system to measure its throughput under specific operating conditions.

binary format --
A file that is in a form that can only be interpreted by a particular system or application.

binding --
The process by which a client locates the server that shares the information desired, and then sets up communication with that server.

bitmap --
A picture or other graphical image that is stored as a series of bits (0s and 1s, each representing a single dot in the image). A bitmap can represent only two colors (usually black and white).

block --
A contiguous group of bytes on a disk that you can access with a single address. By default, 1024 bytes. The size of a block can differ between computers, file system sizes, or devices.

block I/O --
(programming) A data transfer method used by drivers for block access devices. Block I/O uses the system buffer cache as an intermediate data storage area between user memory and the device.

block and character interface --
(programming) A collection of driver routines, kernel functions, and data structures that provide a standard interface for writing block and character drivers.

block data transfer --
(programming) The method of transferring data in units (blocks) between a block device such as a magnetic tape drive or disk drive and a user program.

block device --
(programming) A device, such as a magnetic tape drive or disk drive, that conveys data in blocks through the buffer management code. Compare character device.

block device switch table --
(programming) The table constructed during automatic configuration that contains the address of each block driver entry point routine [for example, open(D2), close(D2), strategy(D2)]. This table is called bdevsw and its structure is defined in the conf.h header file.

block driver --
(programming) A device driver, such as for a magnetic tape device or disk drive, that conveys data in blocks through the buffer management code (for example, the buf structure). One driver is written for each major number employed by block devices.

boot --
The process by which the operating system is started. The kernel must bootstrap itself from secondary storage into an empty machine. No login or process persists across a boot.

boot block --
The first block of a filesystem reserved for a boot program.

boot device --
(programming) The device that stores the self-configuration and system initialization code and necessary filesystems to start the operating system.

bootable object file --
(programming) A file that is created and used to build a new version of the operating system.

BOOTP --
Bootstrap Protocol, the Internet protocol that allows a client host machine to obtain its network configuration information (for example, its IP address) from a configuration database on a BOOTP server.

boot program --
Loads the operating system into main memory See also core.

bootstrap --
(programming) The process of bringing up the operating system by its own action. The first few instructions load the rest of the operating system into the computer.

bottom level --
(programming) Lowest of the four lower RPC levels; programs written to this level can control many transport-specific details.

bounced mail --
E-mail that is returned to the sender as undeliverable.

Bourne shell --
A UNIX system shell, named after its author, Steven R. Bourne. To start a Bourne shell from the command line, type sh and press <Enter>. See also C shell and Korn shell.

bridge --
A device used at the Data Link layer that selectively copies packets between networks of the same type.

broadcast address --
An Internet Protocol (IP) address used to send a message to all the systems on a given network (that belong to the same class).

buffer --
1. An area of computer memory used to store information temporarily before it is written out to a more permanent location, like a file. 2. (programming) A staging area for input-output (I/O) processes where arbitrary-length transactions are collected into convenient units for system operations. A buffer consists of two parts: a memory array that contains data from the disk, and a buffer header that identifies the buffer.

button --
A button on a mouse or a graphical representation on the screen of a push button. You can position the mouse pointer on an onscreen button and click to ``push'' the onscreen button, thus initiating the corresponding action.