[Turing_Machine]

> 7-bit ascii was common (5 characters would fit in a word, like my username GUMBY), as were six bit bytes (pack six characters into a word)

There were a bunch of different six bit character encodings, often (though not always strictly correctly) called "BCD". The horror show of IBM's EBCDIC was an eight bit extension of one of these.

Then there was 5 bit Baudot code, and...

The last time I checked, many *nix systems will still assume that you're on a 5 bit Baudot (uppercase only) teletype (i.e., a genuine physical tty) if you attempt to log in using all uppercase in your user name.

Some systems hacked in more characters by having special "shift in" and "shift out" characters. If a "shift in" character appeared in the stream, the system would switch to the alternate character set until a "shift out" character was received.

[kps]

  > … *nix systems will still assume that you're on a 5 bit Baudot (uppercase only) teletype …

Akshully the original 1963 version of ASCII¹, which was a 7 bit code but did not include lower case. The Model 33 teletype² (one of the terminals used by UNIX developers³, and probably a contributing factor to two-character command names) was a 1963-ASCII device. Even after 1967 ASCII added lower case, popular low end video terminals⁴ did not include it so that they could get away with 6 bits worth of printable character ROM.

¹ http://worldpowersystems.com/archives/codes/X3.4-1963/index....

² https://en.wikipedia.org/wiki/Teletype_Model_33

³ https://commons.wikimedia.org/wiki/File:Ken_Thompson_(sittin...

⁴ https://en.wikipedia.org/wiki/ADM-3A