how many bits count? does the flag bit count in the decimal IBM 1620? It indicated the high order digit of a decimal number, and nothing else. There was a character "record mark" for indicting the right end of a character type field. nb, in the model 2 machine, the flag also indicated the special feature index register, if any.
<https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail> Virus-free.www.avast.com <https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail> <#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2> On Tue, Sep 29, 2026 at 4:10 PM Fred Cisin via cctalk <[email protected]> wrote: > >> Now I have to decide whether the Dnepr-1 counts as 26 bits for my list > ... should parity/sign count?? Oh, and I was missing a 29-bit example ... > so more checking to do (you never know, it might have imagined it!) > > > On Tue, 29 Sep 2026, Paul Koning via cctalk wrote: > > That's certainly a start but just the bare beginning. I suspect that, > unti lthe IBM/360, most machines had word lengths not a power of two. For > example, none of the DEC machines before the PDP-11. Older IBM machines > had assorted word sizes; CDC and Burroughs ditto. I worked on a 1970s era > Philips machine with 24 bits, and there were other minicomputer with that > word length (Modcomp?). Electrologica had 27 bit words. The MC research > machines had word lengths of 30 and 34 bits (the 34 bit one, ARMAC, was a > successor of the 30 bit ARRA 2 with a very similar instruction set, two > instructions per word, but the address space grew from 1k to 4k so the word > was made 4 bits larger). ENIAC was 40 bits I think. > > I would count the sign since it's part of the data representation, but > not the parity bit. And on Burroughs mainframes the 3 tag bits are usually > not mentioned; if you do include them (sensible, since they carry semantic > information) you end up with a word size of 51 bits. Not often you run > into prime numbers for the word size. > > In general, parity is not counted. > 5150: 9 chips per row for "8 bit plus parity" > > In 1982, I bought a 192K ecc memory board for 5150, from Boulder Creek > Systems (civic auditorium balcony of West coast computer Faire) > THAT was called "8 bit", but used TWELVE chips per row for Hamming ECC) > > -- > Grumpy Ol' Fred [email protected] > -- --Carey
