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Tag Wiki '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 typesetting.


History
The limit of the line length in 70–80 characters may well be 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. The most widespread and standard paper size in the US (8.5×11") also has been imposing limitations on the line length: it is possible to print only 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 1 to 1.5 inches 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 punched card could consist of only 80 characters. The widespread computer terminals such as IBM 3270 followed this limitation, their monitors could show only 80 CPL (but with the various number of lines), though with some terminals this number was either reduced by half to 40 CPL, limited to 64 CPL (SWTP CT-64, with 16 lines Https://www.cs.ubc.ca/~hilpert/e/SWTPCT64/index.html" target="_blank" rel="nofollow"> CT-64), or optionally increased to 132 CPL (DEC VT100 family, with 14 lines VT100). Such line lengths have been carried over into text modes of personal computers.

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

RFC 2046 Media Types November 1996

   A. Collected Grammar ....................................   43
     

1.  Introduction
     

   The first document in this set, RFC 2045, defines a number of header
   fields, including Content-Type. The Content-Type field is used to
   specify the nature of the data in the body of a MIME entity, by
   giving media type and subtype identifiers, and by providing auxiliary
   information that may be required for certain media types.  After the
     
, which defines the text/plain [[MIME type]], is itself a 72 CPL plain text. Top of page 3


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

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

Java Google Java Style

Common Lisp Style Guide Google Common Lisp Style Guide

FORTRAN 90

Blink Blink Coding Style Guidelines

Moodle Coding Style

Mono Mono Coding Guidelines
Go Effective Go


Human perception
A study at Wichita State University found that CPL had only small effects on readability, including factors of speed and comprehension. When asked for preferences, however, 60% of respondents indicated a preference for either the shortest (35 CPL) or longest (95 CPL) lines used in the study. At the same time, 100% of respondents selected either one of these quantities as being the least desirable.


See also
  • IBM 80-column punched card format

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