^X (was: an odd question

From: Mark Green <mark_at_cs.ualberta.ca>
Date: Thu Aug 9 21:13:20 2001

> >
> > Ding ding ding, you win. ^G rings the bell. However the original
> > question
> > was the notion of "Control and G" keys contracted to CTRL-G (tty
> > nomenclature)
> > to ^G.
> >
>
> I always assumed it had to do with 6-bit character set implementations.
>
> On the CDC Cybers, which used a 6-bit character set, the peripheral
> processors could be switched to a 7-bit mode, where lowercase
> characters were translated into those 2-character sequences, and
> vice-versa. I cant recall the exact scheme, but i seem to recall
> 2 different prefix characters being used...
>
> Anyways, as i say i cant recall the Cyber character set... but it was
> something like ^A would be translated to a lowercase a, and the ^
> sort of switched bit 7 on (or xored it, or however you want to
> think of it). And if you think of the ASCII character set, ^A would
> be a control-A if bit 7 was switched from the capital A character.
> and referring to ^a instead of ^A would normally be a mistake made
> by people who dont realize that lowercase is inherently inferior ;)
>

The CDC Cyber series had many different character sets, which was a
major pain in the ass for anyone maintaining software for them. I
spent several years working on the Pascal compiler for the CDC
machines (the orignal implementation from ETH). The initial character
sets had 63 characters with 0 reserved for end of line. Later
they moved to 64 characters, with zero being :. The made the end
of line (remember this was the days of punched cards and line
printers) marker very complicated. It was two or more zero characters
that appeared at the end of a word (60 bit words, 10 characters
per word). End of line testing was a real pain.

Later they switched to a mixed 6 bit / 12 bit character scheme that
made life even more complex. Determining the length of a string (in
characters) involved interpreting each character in the string, you
couldn't simply look at the amount of memory used.

I spent many pleasant (and not so pleasant at times) years
doing systems programming on those machines. The real scary
thing is I still remember details of it, even after 25 years.
Received on Thu Aug 09 2001 - 21:13:20 BST