22 Sep
2004
22 Sep
'04
11:13 a.m.
--- Lyle Bickley <lbickley(a)bickleywest.com> wrote:
The IBM 7070 was modeled after the IBM 650 - so the
7070 was a bi-quinary (2
out of 5) encoded machine.
Do you know why a bi-quinary encoding was used instead
of the more obvious 8-4-2-1 BCD encoding scheme? I've
been a bit curious about that. More generally, I've
been curious why decimal architectures held on for so
long, given the higher cost of the CPU logic. In the
older semi-electronic punch-card calculators, it
clearly simplified the logic overall, as they were
running simple hard-wired (plug-board) programs
interfacing with decimal-oriented electromechanical
input and output. I can also see where it made sense
on smaller digit-serial designs. In a large-scale
parallel CPU, however, it's not clear to me why
a binary architecture (doing binary to decimal
conversion in software) wasn't preferred right from
the start.
--Bill