Editing Computer file (section)

==Storage==
Any file that has any useful purpose must have some physical manifestation. That is, a file (an abstract concept) in a real computer system must have a real physical analogue if it is to exist at all.

In physical terms, most computer files are stored on some type of data storage device. For example, most [[operating system]]s store files on a [[hard disk]]. Hard disks have been the ubiquitous form of [[non-volatile]] storage since the early 1960s.<ref name="Mee">Magnetic Storage Handbook 2nd Ed., Section 2.1.1, Disk File Technology, Mee and Daniel, (c)1990,</ref> Where files contain only temporary information, they may be stored in [[RAM]]. Computer files can be also stored on other media in some cases, such as [[magnetic tape]]s, [[compact disc]]s, [[Digital Versatile Disc]]s, [[Zip drive]]s, [[USB flash drive]]s, etc. The use of [[solid state drives]] is also beginning to rival the hard disk drive.

In Unix-like operating systems, many files have no associated physical storage device. Examples are {{Mono|[[/dev/null]]}} and most files under directories {{Mono|/dev}}, {{Mono|/proc}} and {{Mono|/sys}}.  These are virtual files: they exist as objects within the operating system kernel.

As seen by a running user program, files are usually represented either by a [[File Control Block|file control block]] or by a [[file handle]]. A file control block (FCB) is an area of memory which is manipulated to establish a filename etc. and then passed to the operating system as a parameter; it was used by older IBM operating systems and early PC operating systems including [[CP/M]] and early versions of [[MS-DOS]]. A file handle is generally either an [[opaque data type]] or an integer; it was introduced in around 1961 by the [[ALGOL 60|ALGOL-based]] [[Burroughs MCP]] running on the [[Burroughs B5000]] but is now ubiquitous.