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Characters per line
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In and , characters per line ( CPL) or terminal width refers to the maximal number of characters that may appear on a single . It is similar to in .


History
The limit of the line length in 70–80 characters may well have originated from various technical limitations of various equipment. The American could type only 72 CPL, while the British ones even less, 70 CPL. In the era of , most designs of the typewriter carriage were limited to 80–90 CPL. Standard paper sizes, such as the international standard A4, also impose limitations on line length: using the US standard Letter paper size (8.5×11"), it is only possible to print a maximum of 85 or 102 characters (with the font size either 10 or 12 characters per inch) without margins on the typewriter. With various margins – usually from for each side, but there is no strict standard – these numbers may shrink to 55–78 CPL.

In computer technology, a line of an IBM consisted of 80 characters. Widespread computer terminals such as DEC's VT52 and VT100 mostly followed this standard, showing 80 CPL and 24 lines. This line length was carried over into the original 80×25 text mode of the IBM PC, along with its clones and successors. To this day, virtual terminals most often display 80×24 characters.

The "long" line of 132 CPL comes from mainframes' .

(2023). 9780132704342 .
(2023). 9780203508961 .
However, some printers or printing terminals could print as many as 216 CPL, given certain extra-wide paper sizes and/or extra-narrow font sizes.


In modern computing
With the advent of desktop computing and publishing, and technologies such as used in and , a uniform CPL has been made mostly obsolete. (and some other modern text presentation formats) uses dynamic which is more flexible than characters per line restriction and may produce a text block with non-rectangular shape, just like in paper .

Many documents still conform to 72 CPL out of tradition (e.g., ).


In programming
Many style guides for computer programming define the maximum or desirable number of characters in a line of :
Ada Ada 95 Quality and Style Guide

Agda agda/agda-stdlib: Style guide for the standard library

Python PEP 8 Style Guide for Python Code Style Guide for Python Code

CCM4 CCM4 self-imposed limit
Android Android Code Style Guidelines for Contributors

Common Lisp Style Guide Google Common Lisp Style Guide

Java Google Java Style

Rust (rustfmt default) rustfmt Documentation

Racket How to Program Racket: a Style Guide
FORTRAN 90 (until 2023)

Blink Blink Coding Style Guidelines

Moodle Coding Style

Mono Mono Coding Guidelines
Go Effective Go

(JavaScript has no official style guide)


See also
  • IBM 80-column punched card format
  • Apple 80-Column Text Card
  • Column (typography)
  • (the equivalent concept for non-monospaced text)

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