[rescue] Al Kossow rocks the world!

Skeezics Boondoggle skeezics at q7.com
Sat Apr 24 15:59:13 CDT 2004

Bill had asked for some PERQ pictures a while back... here are some wholly 
unimpressive shots of my completely disorganized basement offered for now 
without commentary:


But more importantly, Al Kossow has some _gorgeous_, very high res shots 
of a PERQ board set:


These are huge - about 3500x4200 pixels, ~ 2MB each to download - but
they're lovely.  I wish I had a decent output device to print these out
and frame them. :-)  I'll have to pull out some of the boards in my
machines; they're different revs.  I have a 2MB ICL-built memory board
where the DRAMs are all piggybacked on top of each other - it's bizarre.  
And I've got a wire-wrapped CMU-built 3Mbit Ethernet board, from back when
the PERQs and Altos shared a wire and have the traffic over the ARPAnet
was MazeWar packets. :-)

But he floored me with a document that I'd never seen before (and I have
quite a collection of obscure PERQ docs in storage) - a chip-level
description of the PERQ CPU.  Combined with the microprogrammers reference
guide (and those glorious pictures of the CPU board itself :-) you can get
a complete understanding of how the thing was built:


I used to love to tweak 8086 guys about their 4 puny registers - the PERQ
CPU has 256 general-purpose 20-bit registers.  What I didn't realize was
that the "dual ported" register file was actually implemented as two
complete sets of registers, with some goofy magic to write each half in
parallel - apparently a technique used in the PDP-11 and some other
processors of the day - so that you could read two registers and feed them
to the ALU in the same cycle and avoid the cost of expensive dual-ported
SRAMs?  I was up until 3AM reading this document, and was exhausted but
completely enthralled.  Non-collectors just can't understand what a
feeling that is.  :-)

-- Chris

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