An Operating Systems Vade Mecum

Glossary 339I/O. Either input or output. (See Transput.)IOP. Input-output processor. Also called channel.Kernel. The core of the operating system; a permanently resident control program usingspecial hardware privileges to react to interrupts from external devices and to requests forservice from processes. (See Essential utility and Optional utility.)Kernel space. The virtual space of the kernel.Kernel time. Time spent by the kernel making policy decisions and carrying them out.Key. (1) A security mechanism used with locks. (See Lock.) (2) The first element in apair that is used for searching for that pair in a directory. (3) A field of a file record usedfor searching for that record.Knot. A set of vertices in a generalized resource graph such that starting at any vertex ofthe knot, paths lead to all the vertices in the knot and to no vertices outside the knot.Label. An initial file on a magnetic tape that describes the tape.Latency. Delay between a request and its completion. (See Seek latency, Windinglatency, and Rotational latency.)Law of Diminishing Returns. The first policy you think of is very poor. The next oneworks fine. With enormous effort, you can do even a little better.Lazy evaluation. Avoiding doing work when it is first discovered in the hope that itmight never be needed. (Example: Copy on write. Opposite of Eager evaluation.)Level Principle. What appears as an active entity from one point of view often appearsas a data structure from a lower level.Liberal. A resource allocation policy is liberal if it grants resources whenever asked.Liberality is intended to maximize the level of multiprogramming. (Opposite of Conservative.)Line editor. An interactive program used to enter and modify the contents of a singleline. This program is often part of the terminal driver. (See Editing.)Line clock. A device that generates an interrupt every 60th (or 50th) of a second.Linker. The program that combines the output of compilers or assemblers with libraryroutines and prepares a load image.Livelock. A situation in which the algorithm that decides whether to block an activityfails to reach a decision and continues to use computational resources. (See Deadlockand Starvation.)Load. To construct a new process, initializing its virtual store, including its instructionsand data, from a load image. (See Split.)Loader. A program that brings a load image into main store. Also called Image activator.Load image. A representation of the virtual space for a process, usually kept in a file.This file is constructed by a linker and brought into main store by a loader.