File Control Block: Difference between revisions

Revision as of 09:00, 7 January 2014

Revision as of 04:44, 30 April 2014

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A '''File Control Block''' ('''FCB''') is a file system structure in which the state of an open [[Computer file|file]] is maintained. An FCB is managed by the operating system, but it resides in the memory of the program that uses the file, not in operating system memory. This allows a programprocess to have as many files open at one time as it wants to, provided it can spare enough memory for an FCB per file.

The FCB originates from [[CP/M]] and is also present in most variants of [[DOS]], though only as a backwards compatibility measure in [[MS-DOS]] versions 2.0 and later. A full FCB is 36 bytes long; in early versions of CP/M, it was 33 bytes. This fixed size, which could not be increased without breaking application compatibility, lead to the FCB's eventual demise as the standard method of accessing files.