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.