On 29/09/2026 20:18, Paul Koning wrote:
That's certainly a start but just the bare beginning.
Very true.
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.
I went to a (guest) lecture by Dijkstra once, where he mentioned
semaphores and the X8, so quite how I missed that one I just don't know!!
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.
I have the B5000 for 48-bit and the B6500 for 51-bit. It does get a bit
tricky though when trying to decide what's what. I suppose 60 years of
development blurs the lines a bit as things progress.
Wikipedia has the Gemini guidance computer as 13-bit, the Odra 1001 is
17-bit (although I'm relying on Google Translate iirc), 23-bit and
29-bit were in that list just now, and then the 51-bit B6500. There's an
infinite gap to fill above the 60-bit CDC6600, but given the costs (at
least before) 8/16/32 became standard, I suspect that most of that gap
will be forever empty.
Requesting candidates for two-bit computers is just asking for trouble :-)
Antonio
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Antonio Carlini
[email protected]
