In computing, plain text is a term used for an ordinary "unformatted" sequential file readable as textual material without much processing.

The encoding has traditionally been either ASCII, one of its many derivatives such as ISO/IEC 646 etc., or sometimes EBCDIC. No other encodings are used in plain text files which neither contain any (character-based) structural tags such as heading marks, nor any typographic markers like bold face, italics, etc.

Unicode is today gradually replacing the older ASCII derivatives limited to 7 or 8 bit codes. It will probably serve much the same purposes, but this time permitting almost any human language as well as important punctuation and symbols such as mathematical relations (≠ ≤ ≥ ≈), multiplication (× •), etc, which are not included in the more restricted ASCII set.

Usage

The purpose of using plain text today is primarily a "lowest common denominator" independence from programs that require their very own special encoding or formatting (with due sacrifices and limitations). Plain text files can be opened, read, and edited with most text editors. Examples include Notepad (Windows), edit (DOS), ed, vi, vim or Gedit (Unix, Linux), SimpleText (Mac OS), or TextEdit (Mac OS X). Other computer programs are also capable of reading and importing plain text. It can also be used by simple computer tools such as line printing text commands like type (DOS and Windows) and cat (Unix).

Plain text files are almost universal in programming; a source code file containing instructions in a programming language is almost always a plain text file. Plain text is also commonly used for configuration files, which are read for saved settings at the startup of a program.

Related terms

The related term, plaintext, is most commonly used in a cryptographic context, while cleartext usually refers to lack of protection from eavesdropping. Usage of these terms is such that there is some confusion amongst them, especially among those new to computers, cryptography, or data communications.

Philosophy

This reveals that plain text is in fact the technical user's way to regard a file or a sequence of bytes. In this sense, there is no plain text, since bits are stored as states of latches, charges on transistor gates, microscopic magnetic or mechanical dots on a disk, etc, and humans don't have the senses needed to read this. The information must thus appear as text (on screen or on paper) in order to be text in this absolute sense of the word.

Plain text is a way to represent generic text without attributes such as fonts, subscripts, and boldface; due to this simplicity, it is readable and processable by almost any computer program. In a way a HTML, SGML and an XML file is regarded as plain text, since no control codes (see below) are used, but real structural tags are actually included in these formats. As regards to the SGML and XML author, these tags are "human readable" since that format author understands the structure by reading the format. This may illuminate the complications of the usage of terms within computer science: it's all a relative view point.