Definition: file

A collection of bytes stored as an individual entity in every computer-based desktop and mobile device. A file is the common denominator of storage. All data and programs, no matter which kind, are stored as files with an assigned file name that must be unique within the storage folder it resides in. Files with the same name can reside in separate folders. See folder.

Computers Know Nothing About Data Files
To the computer, a data file is nothing more than a string of bytes that is identified by name and location in storage. Once read into the computer's RAM, the structure of a file is known to the software that manipulates it. For example, database files are made up of a series of rows (records) such as one per customer, vendor or transaction. Word processing files contain a continuous flow of text interspersed with format codes (tags).

Except for ASCII text files, which contain only raw text, all data files have proprietary structures. Formatting and descriptive information are contained in headers at the beginning of the file and/or in tags interspersed throughout the file. XML is an example of a very popular tagged text file. See metadata and XML.

Computers Do Understand Program Files
In contrast to data files, the computer is inherently aware of the content of an executable program file, which contains machine instructions. When read from storage and written into RAM, the computer is given the starting byte in RAM, and it expects to find the machine language it recognizes, one instruction following the other (see machine language). Otherwise, it will not execute the program (see abend).

Everything Stored Is a File

The common unit of storage no matter what the application is the file.

File Contents
Following are the major file types and the data structures they contain. See file association, ASCII file, file system and files vs. folders.

 Data
 File Type       Contents

 data file       text & binary
  (table)         (rows/records)

 document        text & format codes

 spreadsheet     rows/columns of cells

 image           rows/columns of pixels

 drawing         list of vectors

 CD audio        digitized sound waves

 compressed
  audio (MP3,    compressed digitized
  AAC, etc.)     sound waves

 MIDI            MIDI instructions

 video           MPEG frames

 Web page        text, HTML tags &
  (HTML file)     JavaScript

 XML file        text

 batch file      text

 text file       text


 Software
 File Type       Contents

 source code     text

 intermediate
  language       binary bytecode

 executable
  program        binary machine language

Lotsa Files

Files add up quicker than people realize. A virus scan in 2024 of this Mac identified more than a million files. Hard to believe such a large quantity exists with only 50 apps installed in the machine.