An Operating Systems Vade Mecum

Glossary 349Task. A thread of control within the kernel.Text. The contents of a file intended to be read by humans.Text editor. An interactive program used to enter and modify the contents of a text file.(See Editing.)Thrashing. The situation in which computation is blocked most of the time waiting fordata to be transferred between two levels of the storage hierarchy. The usual case isthrashing due to page traffic between main and backing store.Thread. An active entity that inhabits a process. Programming-language ‘‘processes’’are often implemented as threads.Tie down. Mark a segment or page as not susceptible to swapping out or shuffling, usuallybecause DMA is in progress. Also called lock, pin down,orfix.Time. The resource of instruction execution, which the operating system shares amongthe various processes that are competing for it.Timeout. A parameter that indicates how long an activity is willing to wait for a particularevent.Timesharing. Usually refers to interactive multiprogramming. We do not use this term.Timestamp. A field that records the time at which some event happened.Track. A band on the platter of a disk pack.Transaction. A group of file accesses (or other transput operations) that together accomplisha goal. (See Synchronization atomicity, Failure atomicity, and Permanence.)Transaction manager. The module of the kernel that provides transaction services.Transfer latency. The amount of time needed for a sector to pass under the read/writehead of a disk.Translation look-aside buffer. A cache used by the hardware to hold the most frequentlyused parts of the translation table.Translation table. A table used by the hardware to assist in performing address translation.(See Page table and Segment table.)Transparent. Invisible or indistinguishable to a process. Transput is transparent withrespect to a device if the process need not know which device is being used. Addresstranslation is transparent to processes under paging.Transput. Either input or output. Transput is often called I/O, which stands forinput/output.Transput-bound. A process is transput-bound if it spends most of its time waiting fortransput to complete. An operating system is transput-bound if the ready list is usuallyempty and the transput wait lists have members. (Opposite of Compute-bound.)Trap. A hardware event that signals a program error such as division by zero or accessingan invalid virtual address. The service-call instruction also causes a trap. Trapscause a context switch to the kernel.