An Operating Systems Vade Mecum

348 GlossaryStarvation. The situation in which a process continues to be denied a resource that itneeds, even though the resource is being granted to other processes.Starvation detection. Noticing starvation situations when they arise and treating themby preventing new processes from acquiring resources.State vector. Part of the context block that the operating system keeps available at alltimes. It stores the contents of registers while the process is not running.Steady state. The situation that holds after the load has been constant for a long enoughtime that average behavior has begun to occur.Storage module. The part of the operating system kernel that makes and implementsmain-store allocation policy.Store-synchronous. A class of mutual-exclusion and synchronization methods that relyon the fact that main store services only one request at a time, even on a multiprocessor.(Opposite of Processor-synchronous.)Structured file. A file built of records, some of whose fields are treated as keys.Structure editor. An interactive program used to enter and modify the contents of anobject such as a printer font or a VLSI layout. (See Editing.)Subdisk. A region of the disk introduced to promote clustering. An attempt is made tokeep files entirely within subdisks.Subject. An entity such as a process or a user that wishes to access an object. (SeeAccess control.)Swapping. Moving part of or all the virtual store of a process between main and backingstore. The area on backing store reserved for this purpose is called swapping space. Aprocess (or page or segment) on backing store is swapped out. A process (or page or segment)in main store is swapped in.Switch. (1) See Process switch and Context switch. (2) A variable used to determinewhich of two conflicting activities may next enter a region. (See Non-alternating switchand Spin lock.)Synchronization. (1) Achieving a common notion of time, either by sharing clocks orby passing information. Synchronous transmission uses a header to achieve commonclocks. (2) Causing an activity to wait for a condition.Synchronization atomicity. A property of transactions that each one is atomic, that is,indivisible, immune to interference from other transactions that might be occurring at thesame time. (See Failure atomicity.)Synchronization graph. A graph whose nodes are activities and whose arrows are precedenceconstraints. Also called precedence graph.Synchronous communication. The situation where a process that has requested a sendor receive is blocked until the request completes. (Opposite of Asynchronous communication.)Synchronous transput. The situation where a process that has requested transput isblocked until the transput completes. (Opposite of Asynchronous transput.)