Files, Implements

A computer file is a piece of arbitrary information, or resource for storing information, that is available to a computer program and is usually based on some kind of durable storage. more...

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A file is durable in the sense that it remains available for programs to use after the current program has finished. Computer files can be considered as the modern counterpart of the files of printed documents that traditionally existed in offices and libraries, which are the source of the term.

File contents

As far as the operating system is concerned, a file is in most cases just a sequence of binary digits. At a higher level, where the content of the file is being considered, these binary digits may represent integer values or text characters, or anything else; Turing completeness shows that the bits might represent anything. It is up to the program using the file to understand the meaning and internal layout of information in the file and present it to a user as a document, image, song, or program.

At any instant in time, a file might have a size, normally expressed in bytes, that indicates how much storage is associated with the file. In most modern operating systems the size can be any whole number up to a system limit. However, the general definition of a file does not contain its instant size as having any real meaning, unless the data within the file happens to correspond to data within a pool of persistent storage.

For example, the file to which the link /bin/ls points in a typical Unix-like system probably has a defined size that seldom changed. Compare this with /dev/null. This is a file, but its size may be open to question.

Information in a computer file can consist of smaller packets of information (often called records or lines) that are individually different but share some trait in common. For example, a payroll file might contain information concerning all the employees in a company and their payroll details; each record in the payroll file concerns just one employee, and all the records have the common trait of being related to payroll—this is very similar to placing all payroll information into a specific filing cabinet in an office that does not have a computer. A text file may contain lines of text, corresponding to printed lines on a piece of paper. Alternatively, a file may contain an arbitrary binary image (a BLOB) or it may contain an executable.

The way information is grouped into a file is entirely up to the person designing the file. This has led to a plethora of more or less standardized file structures for all imaginable purposes, from the simplest to the most complex. Most computer files are used by computer programs. These programs create, modify and delete files for their own use on an as-needed basis. The programmers who create the programs decide what files are needed, how they are to be used and (often) their names.

Read more at Wikipedia.org