Your description fits PERFECTLY a Heathkit / Zenith Data Systems Z-100
series computer (actually, Z-110 or Z-120 series). I am sure, from you
description, that this is what it was. It's actually a very common system
as S-100 systems go .... about 100,000 were built, five to ten times more
than Imsai or SOL-20 systems.
All of the S100 systems I've seen to date have comprised a backplane
and then cards for various system components - including CPU and
memory. However, I unearthed one today which held much of the system
logic on the backplane itself (i.e. more like a modern-day PC
motherboard - I'd heard such things existed, but this is the first one I've
actually seen).
Unfortunately I forgot to bring the thing home with me,
so I'm a bit
light on remembered details (but can get more tomorrow if needs be).
However, it appeared to have both an 8088 and 8085 CPU on board,
memory, what is probably ROM, a handful of S100-bus [1] connectors,
parallel port, a light-pen port (unusual!), plus a few other ports (at
least one was serial I expect). There were a few other IDC-style pin
headers too - perhaps for some sort of storage, but none of them were
obviously
labeled as to function.
Sound familiar to anyone?