An Operating Systems Vade Mecum

Glossary 341Mode. See Access mode.Model. A mathematical description of a physical situation, used for deriving analytic orsimulation results.Monitor. A programming-language construct for mutual exclusion and synchronization.Mounting. Placing the contents of one disk as a virtual subdirectory in another disk.Multicomputer. A computer built of several processors that do not share main store.The processors communicate by sending messages through a communication device.Multiprocessor. A computer built with more than one processor sharing the same mainstore. Also called attached processor.Multiprogramming. The situation in which many processes may be in the ready list atone time and share the computational resource through some policy of short-termscheduling.Mutual exclusion. Ensuring that two activities that use the same data may not occur atthe same time. (See Region.)Name space. The set of identifiers in a program, representing variables and procedures.Network. A number of computers connected by communication lines for the purpose oftransmitting data.Nickname. A simple way to invoke a complex operation.Non-alternating switch. A device used to determine which of two conflicting activitiesmay enter a region.Non-preemptive. A policy that never preempts a resource from a process.Non-privileged state. See Processor state.Object. A unit of information that a subject wishes to access. (See Access control.)Offline. (1) A device is offline if it is disconnected from the computer and no transferscan be made. (2) A set of operations is performed offline if they may be done at any convenienttime instead of at the time they are requested.Offset. An address given as the distance from the beginning of some object, often a segmentor page.One-level structure. A one-level file structure has one directory for all file names. Alsocalled flat.One-shot allocation. A resource allocation policy that requires each process to acquireall the resources it needs at one time. Also called preclaiming.Operating system. Software for a computer, including the kernel, essential utilities, andoptional utilities.Operator. An employee of a computer installation in charge of loading jobs and collectingoutput.Open. (1) To initialize data structures or hardware when a data object or device starts tobe used. (2) A process that wishes to use a resource (like a file) might open the resourcebefore it starts. (See Descriptor.)