The limit of the line length in 70–80 characters may well have originated from various technical limitations of various equipment. The Americanteletypewriters could type only 72 CPL, while the British ones even less, 70 CPL.[1] In the era oftypewriters, most designs of the typewriter carriage were limited to 80–90 CPL. Standard paper sizes, such as the international standardA4, also impose limitations on line length: using the US standardLetter 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 12characters per inch) without margins on the typewriter. With various margins – usually from 1–1.5 inches (25–38 mm) for each side, but there is no strict standard – these numbers may shrink to 55–78 CPL.
In computer technology, a line of an IBMpunched card consisted of 80 characters. Widespread computer terminals such as DEC'sVT52 andVT100 mostly followed this standard, showing 80 CPL and 24 lines. This line length was carried over into the original 80×25text mode of theIBM 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'line printers.[2][3][4] 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.[5]
With the advent of desktop computing and publishing, and technologies such asTrueType used inword processing andweb browsing, a uniform CPL has been made mostly obsolete.HTML (and some other modern text presentation formats) uses dynamicword wrapping which is more flexible than characters per line restriction and may produce a text block with non-rectangular shape, just like in papertypesetting.
Manyplain text documents still conform to 72 CPL out of tradition (e.g.,RFC678).
