A monospaced font, also called a fixed-pitch or non-proportional font, is a font whose letters and characters each occupy the same amount of horizontal space.[1] This contrasts to variable-width fonts, where the letters differ in size to one another.
The first monospaced typefaces were designed for typewriters, which could only move the same distance forward with each letter typed. This also meant that monospaced fonts need not be typeset like variable width fonts and were, arguably, easier to deal with.
Note that this article generally assumes Western (Latin-based, Cyrillic, or Greek) writing systems. East Asian rules of typography, for example, require CJK fonts to always be monospaced at least as far as the main characters for writing words (i.e. not punctuation) are concerned. Other scripts vary in their use of monospaced fonts. There is an attempt at a monospaced Arabic font—"Simplified Arabic Fixed".[2]
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Monospaced fonts were widely used in early computers and computer terminals, which often had extremely limited graphical capabilities. Hardware implementation was simplified by using a text mode where the screen layout was addressed as a regular grid of tiles, each of which could be set to display a character by indexing into the hardware's character map. Some systems allowed colored text to be displayed by varying the foreground and background color for each tile. Other effects included reverse video and blinking text. Nevertheless, these early systems were typically limited to a single console font.
Even though computers can now display a wide variety of fonts, almost every commercial IDE and software text editor employs a monospaced font as the default typeface. This increases the readability of source code, which is often heavily reliant on distinctions involving individual symbols. Monospaced fonts are also used in terminal emulation and for laying out tabulated data in plain text documents. In technical manuals and resources for programming languages, a monospaced font is often used to distinguish code from natural language text.
The term modern is sometimes used as a synonym for monospace generic font family. The term modern can be used for a fixed-pitch generic font family name used in OpenDocument format (ISO/IEC 26300:2006) and Rich Text Format.[3][4]
A monospaced font is often used in making ASCII art due to the ability to maintain the alignment of characters which are at the same position in different lines.
This is especially true in Line Drawing, where the characters are blocks and should be fixed-width.
┌─┐ ┌┬┐ [example of line drawing characters]
│ │ ├┼┤ [requires fixed-width, especially with spaces]
└─┘ └┴┘ [otherwise they are mis-aligned, as here.]
Monospaced fonts are preferred for displaying nucleic acid and protein sequences, as they ensure that the representation of every nucleotide or amino acid occupies the same amount of space. Alignment of the letters makes it easier to compare different sequences visually.