Six-bit character code: Difference between revisions

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A '''six-bit character code''' is a [[character encoding]] designed for use on computers with [[word length]]s a multiple of 6. Six bits can only encode 64 distinct characters, so these codes generally include only the upper-case letters, the numerals, some punctuation characters, and sometimes control characters. Such codes with additional [[parity bit]] were a natural way of storing data onThe [[IBM 7 track|7-track]] [[Magnetic tape data storage|magnetic tape]] format was developed to store data in such codes, along with an additional [[parity bit]].

==Types of six-bit codes==

An early six-bit binary code was used for [[Braille]], the reading system for the blind that was developed in the 1820s.

The earliest computers dealt with numeric data only, and made no provision for character data. [[Six-bit BCD]], with several variants, was used by [[IBM]] on early computers such as the [[IBM 702]] in 1953 and the [[IBM 704]] in 1954.<ref>{{cite book |author=IBM Corporation |title=704 electronic data-processing machine: manual of operation |date=1954 |url=http://www.bitsavers.org/pdf/ibm/704/24-6661-2_704_Manual_1955.pdf}}</ref>{{rp|p.35}} ThisSix-bit encodingencodings waswere replaced by the 8-bit [[EBCDIC]] code starting in 1964, when [[System/360]] standardized on 8-bit [[byte]]s. There are some variants of this type of code (see [[#BCD-variants|below]]).

Six-bit character codes generally succeeded the five-bit [[Baudot code]] and preceded seven-bit [[ASCII]]. One popular variant was [[Digital Equipment Corporation|DEC]] SIXBIT. This is simply the ASCII character codes from 32 to 95 coded as 0 to 63 by subtracting 32 (i.e., columns 2, 3, 4, and 5 of the ASCII table (16 characters to a column), shifted to columns 0 through 3, by subtracting 2 from the high bits); it includes the space, punctuation characters, numbers, and capital letters, but no control characters. Since it included no control characters, not even end-of-line, it was not used for general text processing. However, six-character names such as [[filename]]s and [[assembly language|assembler]] [[identifier|symbol]]s could be stored in a single [[36-bit]] word of [[PDP-10]], and three characters fit in each word of the [[PDP-1]] and two characters fit in each word of the [[PDP-8]].