29 Sep
2026
29 Sep
'26
1:03 p.m.
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
--
Antonio Carlini
antonio(a)acarlini.com