30 Sep
2026
30 Sep
'26
8:21 a.m.
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.
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On Tue, Sep 29, 2026 at 4:10 PM Fred Cisin via cctalk <cctalk(a)classiccmp.org>
wrote:
--
--Carey
> 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 cisin(a)xenosoft.com