bit-widths, was Re: HP Laserjet ..again....

[William Maddox]

--- Lyle Bickley <lbickley at 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