Operating System Glossary1 (A to J)

Address Space – The range of addresses available to a computer program

Address Translator – A functional unit that transforms virtual addresses to real addresses

Application Programming Interface (API) – A standardized library of programming tools used by software developers to write applications that are compatible with a specific operating system or graphic user interface.

Asynchronous Operation – An operation that occurs without a regular or predictable time relationship to a specified event; for example, the calling of an error diagnostic routine that may receive control at any time during the execution of a program

Batch Processing – pertaining to the technique of executing a set of computer programs such that each is completed before the next program of the set is started

Block – (1) a collection of contiguous records that are recorded as a unit; the units are separated by interblock gaps. (2) a group of bits that are transmitted as a unit.

Busy waiting – the repeated execution of a loop of code while waiting for an event to occur

Cache Memory – a memory that is smaller and faster than main memory and that is interposed between the processor and main memory.  The cache acts as a buffer for recently used memory locations.

Client – a process that requests services by sending messages to server processes

Cluster – a group of interconnected, whole computers working together as a unified computing resource that can create the illusion of being one machine.  The term whole computer means a system that can run on its own, apart from the cluster.

Concurrent – pertaining to processes or threads that take place within a common interval of time during which they may have to alternately share common resources.

Critical Section – in an asynchronous procedure of a computer program a part that cannot be executed simultaneously with an associated critical section of another asynchronous procedure

Deadlock – (1) an impasses that occurs when multiple processes are waiting for the availability of a resource that will not become available because it is being held by another process that is in a similar wait state

Device Driver – an operating system module (usually in the kernel) that deals directly with a device or I/O module

Direct Memory Access (DMA) – a form of I/O in which a special module, called a DMA module, controls the exchange of data between main memory and an I/O device.  The processor sends a request for the transfer block of data to the DMA module and is interrupted only after the entire block has been transferred.

Disabled Interrupt – a condition, usually created by the operating system, during which the processor will ignore interrupt request signals of a specified class

Disk Cache – a buffer, usually kept in main memory, that functions as a cache of disk blocks between disk memory and the rest of main memory

Distributed Operating System – a common operating system shared by a network of computers.  The distributed operating system provides support for interprocess communication, process migration, mutual exclusion, and the prevention or detection of deadlock.

Enabled Interrupt – a condition, usually created by the operating system, during which the processor will respond to interrupt request signals of a specified class

Encryption – the conversion of plain text or data into unintelligible form by means of a reversible mathematical computation

Execution Context – same as process state

File – a set of related records treated as a unit

File Allocation Table (FAT) – a table that indicates the physical location on secondary storage of the space allocated to a file.  There is one file allocation table for each file.

File Management System – a set of system software that provides services to users and applications in the use of files, including file access, directory maintenance, and access control.

First In First Out (FIFO) – a queuing technique in which the next item to be retrieved is the item that has been in the queue for the longest time

Hash File – a file in which records are accessed according to the values of a key field.  Hashing is used to locate a record on the basis of its key value.

Hashing – the selection of a storage location for an item of data by calculating the address as a function of the contents of the data.  This technique complicates the storage allocation function but results in rapid random retrieval.

Hit Ratio – in a two-level memory, the fraction of all memory accesses that are found in a the master memory (i.e. the cache)

Interrupt – a suspension of a process, such as the execution of a computer program, caused by an even external to that process and performed in such a way that the process can be resumed

Interrupt Handler – a routine, generally part of the operating system.  When an interrupt occurs, control is transferred to the corresponding interrupt handler, which takes some action in response to the condition that caused the interrupt.

Job – a set of computational steps packaged to run as a unit

Job Control language (JCL) – a problem-oriented language that is designed to express statements in a job that are used to identify the job or to describe its requirements to an operating system