18 bit CPU; was: Speed now & then

On 04/12/2018 06:23 AM, Diane Bruce wrote: I could see lots of problems doing it any other way, just from the viewpoint of 'C'. A character on the Cyber 70/170 series is either 6 bits or 12 bits, if extensions are used. That's not to say that in a character string, *all* characters are either 6 bits or 12 bits, but can be a mixture, with certain 6-bit codes used as "escape" codes signaling a 12 bit character code. Two null characters have to be placed in the low-order 12 bits of a word to signal an end of line, so that EOL can be anywhere from 12 to 60 bits. This peculiar convention dates from the time when 6-bit codes were common and included only uppercase letters, digits and a few punctuation. I recall the various papers and proposals that circulated at the time to extend the set. Rather elaborate schemes for packing 8 bit characters into a 60 bit word (7.5 of them), use of 10 and 12 bit codes and the aforementioned 6/12 bit scheme, which was selected because it made the smallest impact to existing programs. Added to that, the machines are ones' complement. And yes, Bill--perhaps I wasn't clear enough, but on SX1100 a char is 8 bits plus sign, hence +/-255, with +/- zeroes. --Chuck