17 Oct
2007
17 Oct
'07
10:28 a.m.
Jim Battle wrote:
Yep - the number of systems which could have hardware FPU support added as an
option must be pretty large, even discounting the IBM-compatible PC world.
(I've had some NS32016 stuff with NS32081 FPU on the bench the last couple of
weeks, for instance).
> What do
you mean by 'smallest computer' by the way? Smallest in terms
> of spec? I'm pretty sure some of the 1950's stuff had optional
> floating point hardware available, although it wouldn't have been
> physically small :)
Northstar (of Northstar Horizon fame) sold an S-100 card that had a TTL
FPU on it. It was a microcoded affair (256 words of 40 bits) that
processed a nibble (BCD digit) per clock (4 MHz I believe). You could
also specify how many digits were in the mantissa (2-14, even # digits
only). Only the four basic functions, +-*/, were supported. Others sold S-100 cards that used an AMD FPU chip.
This too required
poking data bytes and a command, then waiting for the result to be
computed and then pulling out the result bytes. It wasn't somehow
integrated into the instruction set of the host processor.
I suspect most solutions are (were) like that (add-on rather than integrated).
Finally, I recall seeing an article where somebody
took a pocket
calculator chip and essentially poked simulated keystrokes at it and
then decoded the LED driver output to determine the answer. It was very
slow, though, so all it saved was the space of the floating point
library code.
OK, that really appeals to my appreciation of people coming up with
off-the-wall solutions to problems. :-)