An Operating Systems Vade Mecum

330 GlossaryBacking store. The large storage area used for swapping space. Backing store is typicallydisk or drum.Background. A non-interactive process that executes at the same time as otherprocesses owned by the same user but is not waited for by the command interpreter.(Opposite of Foreground.)Backup file. A file that duplicates the contents of another file to protect against accidentaldeletion of information.Bandwidth. The amount of data a communication line can carry every second.Base. (1) A hardware register that indicates the physical address where a segment starts.(2) A program-accessible register that is used as part of effective address calculation forinstructions.Batch. A style of computer use in which programs are invoked and input is presented tothem in a non-interactive way.Baud. The bandwidth of a communication line, measured in the number of transitionsper second.Beautification Principle. An operating system is a set of algorithms that hide the detailsof the hardware and provide a more pleasant environment.Best fit. A space-allocation policy that accepts the region of space that comes closest tomeeting the space requirements. (See First fit.)Binding. (1) Converting an abstract representation into a concrete one. (2) Associatinga logical name with a physical name. (3) Associating an input or bound port with anentry.Bit map. A mechanism for representing chunks of free and used space by associatingone bit with each chunk.Bit mapped display. A kind of display device where each dot on the display is controlledby a bit in main store.Bit-oriented. A protocol that sends any number of bits, even if the number does not fitexactly into bytes. (Opposite of Character-oriented.)Bit stuffing. Insertion of extra bits in a message to prevent the header bit pattern frombeing sent accidentally.Block. (1) The fundamental chunk size for data stored on a disk. (2) To place a processin a wait list. Such a process is said to be blocked.Block device. A device such as the disk that transfers data in fixed-size blocks.Bottleneck. The limiting resource.Boundary tag. A mechanism for delimiting blocks of free and used space that allowsfreed blocks to be coalesced with neighbors and allows free space to be linked together.Bounded. A resource class is bounded if the number of elements in the class is limited.Bounded buffer. A data object shared between producers and consumers of data. (SeeProducer-consumer.)