An Operating Systems Vade Mecum

Glossary 329Access right. Permission for a subject to access an object via a particular access mode.Activate. A line of text interactively entered into the computer is buffered by the operatingsystem until the line has been activated. A typical line activator is the carriage return.Activity. An executing entity, whether a process, a kernel task, an interrupt-driven procedure,or a DMA transfer.Address translation. Converting a virtual address into a physical address. This operationis performed by hardware for the sake of efficiency.Advised paging. A situation in which processes inform the storage manager that a pageshould be swapped in or out.Alias. An alternative file name. Also called a link.Aligned. Starting on a particular boundary.Allocation state. The number of resources held and claimed by each process and thenumber of resources not allocated to any process.Analysis. Mathematical formulation of a set of interrelated objects and derivation oftheir collective behavior.Anomaly. A situation in page replacement where increasing the number of page framesincreases the number of faults.Arbitration. Selection between simultaneous requests to decide which to honor first.Archive. (1) A place where data may be stored, typically slow to access but large incapacity. (2) Long-term storage of large data files, typically on magnetic tape. (3) Totransfer data from a cache to an archive. (See Cache.)Arrival. When a process appears in the view of the short-term scheduler, either becauseit is a new process, because it has finished waiting for transput or some other resource, orbecause the medium-term scheduler has favored it. (Opposite of Departure.)Arrival rate. The rate at which new processes arrive in the ready queue, usuallyrepresented by α. The expected time between arrivals is 1 / α.Asynchronous communication. The requesting process is not blocked while a send orreceive operation undertaken on its request is completed. Instead, it discovers completionby waiting, polling, or virtual interrupt. (Opposite of Synchronous communication.)Asynchronous transput. The requesting process is not blocked while transput undertakenon its request is completed. Instead, it discovers completion by waiting, polling, orvirtual interrupt. (Opposite of Synchronous transput.)Atomic transaction. A set of operations on files that behave as if they all happened atthe same time or, in case of failure, as if none of them has happened at all.Authentication. Discovering the identity of a subject, either to find out whether thatsubject has access rights over some object or to discover which subject created a particularobject.Automatic chaining. Invoking a frequently needed sequence of programs with onecommand.