HP 21xx vs DEC PDP-8 architecture (was Re: HP's not cool? (was Re: pdp-11/60 Semi-Rescue))

From: Eric Smith <eric_at_brouhaha.com>
Date: Mon Nov 22 02:00:45 1999

"Jay West" <west_at_tseinc.com> wrote:
> I dearly love my PDP-8E, but I truely believe the architecture on the HP
> 21MX line to be far more elegant. Not necessarily superior, but certainly
> more elegant. Just my own biased opinion....

Not even particularly more elegant. In a general sense, the architecture is
the SAME. Aside from changing the word size to 16 bits (which is either
two fewer or four more bits than comparable DEC machines), the only big
enhancement is the provision of a second accumulator.

Even the memory addressing works the same way: one bit of memory reference
instructions selects page zero vs. current page, and one bit enables
indirection. The non-memory-reference instructions are
"microcoded" in the same manner as the DEC 12-bit and 18-bit computer
families.

All of HP's clever and original architectural design went into the HP 9100
programmable calculator and the HP 3000 stack-based computer. The HP 21xx
were just a me-too design; Either HP was trying to build a wider PDP-5 or
PDP-8, or a narrower PDP-9.
Received on Mon Nov 22 1999 - 02:00:45 GMT