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Computer file

A file in a computer system is a sequence of bytes stored as a single unit, typically in a file system on a disk or a magnetic tape (but see note [2] below).

"File" is an abstract concept: what appears to be a single file from the point of view of software may in practice be stored as multiple fragments of data at different places on a disk (or even multiple disks).

Files are created by software and usually conform to a particular file format.

An important subclass of file is the "text file". A text file is a sequence of characters organized into lines (or "records") separated by line breaks. The preferred representation of line breaks differs among operating systems. For example, Mac OS uses 0x0d (carriage return), UNIX systems use 0x0a (line feed), Windows uses 0x0d followed by 0x0a, and VMS uses multiple text file types (including the 3 above) with its default being "variable length record" in which each record begins with a 16 bit integer length field specifying the number of characters in the record. To modify a text file, use a text editor. Some text editors can understand multiple systems' line break conventions.

The term "binary file" often refers to any file other than a text file. But note that ultimately even a binary file is just a collection of bits. To modify a binary file directly (that is, without using an application specific to the file format of that file), use a hex editor.

A "special file" is a file system object which is accessed as though it was a file, but the sequence of bytes or characters is supplied or consumed by another process such as a device driver or network interface.

A collection of files is called a folder or a directory.

Notes

  1. A collection of bytes in RAM isn't usually known as a file, unless it's stored in a RAM disk.
  2. Historically it was common for files to be defined as sequences of records. However this is now uncommon except on certain mainframe operating systems. On most systems, the application or a library creates the "record" abstraction from the byte stream according to the file format.

See also file extension.



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