A file may be designed to store an Image, a written message, a video, a computer program, or any wide variety of other kinds of data. Certain files can store multiple data types at once.
By using computer programs, a person can open, read, change, save, and close a computer file. Computer files may be reopened, modified, and copied an arbitrary number of times.
Files are typically organized in a file system, which tracks file locations on the disk and enables user access.
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 analog if it is to exist at all.
Devices in which files can be Stored:
In physical terms, most computer files are stored on some type of data storage device. For example, most operating systems store files on a hard disk. Hard disks have been an example form of non-volatile storage since the early 1960s. 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 tapes, compact discs, Digital Versatile Discs, Zip drives, USB flash drives, 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 /dev/null and most files under directories /dev, /proc, and /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 or by a file handle. A file control block (FCB) is an area of memory that 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-based Burroughs MCP running on the Burroughs B5000 but is now ubiquitous.
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