Editing ASCII (section)

===Bit width===
The X3.2 subcommittee designed ASCII based on the earlier teleprinter encoding systems. Like other [[character encoding]]s, ASCII specifies a correspondence between digital bit patterns and [[character (computing)|character]] symbols (i.e. [[grapheme]]s and [[control character]]s). This allows [[Digital data|digital]] devices to communicate with each other and to process, store, and communicate character-oriented information such as written language. Before ASCII was developed, the encodings in use included 26 [[English alphabet|alphabetic]] characters, 10 [[numerical digit]]s, and from 11 to 25 special graphic symbols. To include all these, and control characters compatible with the [[CCITT|Comité Consultatif International Téléphonique et Télégraphique]] (CCITT) [[International Telegraph Alphabet No. 2]] (ITA2) standard of 1932,<ref>{{cite web |url=http://handle.itu.int/11.1004/020.1000/4.5.43.en.101 |title=Telegraph Regulations and Final Protocol (Madrid, 1932) |access-date=9 Jun 2024 |archive-url=https://web.archive.org/web/20230821020920/https://search.itu.int/history/HistoryDigitalCollectionDocLibrary/4.5.43.en.101.pdf |archive-date=21 August 2023}}</ref><ref name="bdcode">{{cite web |author-last=Smith |author-first=Gil |title=Teletype Communication Codes |publisher=Baudot.net |date=2001 |url=http://www.baudot.net/docs/smith--teletype-codes.pdf |access-date=2008-07-11 |archive-url=https://web.archive.org/web/20080820043949/http://www.baudot.net/docs/smith--teletype-codes.pdf |archive-date=August 20, 2008 |url-status=live }}</ref> [[FIELDATA]] (1956{{citation needed|date=June 2016|reason=My sources state 1957 rather than 1956, but Wikipedia states 1956 in various places. This needs to be sorted out with better sources.}}), and early [[EBCDIC]] (1963), more than 64 codes were required for ASCII.

ITA2 was in turn based on [[Baudot code]], the 5-bit telegraph code Émile Baudot invented in 1870 and patented in 1874.<ref name="bdcode" />

The committee debated the possibility of a [[Shift code|shift]] function (like in [[ITA2]]), which would allow more than 64 codes to be represented by a [[six-bit character code|six-bit code]]. In a shifted code, some character codes determine choices between options for the following character codes. It allows compact encoding, but is less reliable for [[data transmission]], as an error in transmitting the shift code typically makes a long part of the transmission unreadable. The standards committee decided against shifting, and so ASCII required at least a seven-bit code.<ref name="Mackenzie_1980"/>{{rp|pages=215 §13.6, 236 §4}}

The committee considered an eight-bit code, since eight bits ([[octet (computing)|octet]]s) would allow two four-bit patterns to efficiently encode two digits with [[binary-coded decimal]]. However, it would require all data transmission to send eight bits when seven could suffice. The committee voted to use a seven-bit code to minimize costs associated with data transmission. Since perforated tape at the time could record eight bits in one position, it also allowed for a [[parity bit]] for [[error checking]] if desired.<ref name="Mackenzie_1980"/>{{rp|pages=217 §c, 236 §5}} [[8-bit computing|Eight-bit]] machines (with octets as the native data type) that did not use parity checking typically set the eighth bit to 0.<ref name="Sawyer_1995">{{cite book |author-first1=Stanley A. |author-last1=Sawyer |author-first2=Steven George |author-last2=Krantz |title=A TeX Primer for Scientists |url=https://books.google.com/books?id=bXLDwmIJNkUC&pg=PA13 |date=1995 |publisher=[[CRC Press]] |isbn=978-0-8493-7159-2 |page=13 |bibcode=1995tps..book.....S |access-date=October 29, 2016 |archive-url=https://web.archive.org/web/20161222151907/https://books.google.com/books?id=bXLDwmIJNkUC&pg=PA13 |archive-date=December 22, 2016 |url-status=live }}</ref>