Burroughs machines are rare, especially one this old.
Burroughs had a
policy of taking back their old machines in trade, which they would then
destroy to avoid having used machines in competition with their new
Rumor around here is that when it came time to get rid of the old Burroughs,
Burroughs sold a new machine to the university that bid on our old machine
for less than what they had bid on the old machine.
Everyone here assumed it was because Burroughs was pissed that we had
gone with big VAXen; but perhaps that was just the way Burroughs worked.
The A-series computers are stack machines. Its a very
architecture. At the time of the B5000 series it was considered ahead of
its time, but now that architecture is essentially dead. The most recent
new stack machine I know of is the original HP 3000 minicomputer from
the late 70's early 80's. It is inherently difficult to get a stack
machine to run very fast, like today's superscalar microprocessors. But
a stack architecture results in small code. The virtual machine for Java
byte code is a stack architecture.
describes ShBoom, a stack machine designed by
Chuck Moore (aka the inventor of Forth). The theory behind ShBoom, and
his more recent stack machine, is that if you use a wide word (in this
case 32 bits) you can fetch a whole bunch of tiny instructions at once
then blaze through them. In the case of ShBoom, the core runs at 100Mhz
while the external bus runs slower. Since each opcode is a byte, he can
fetch four opcodes at once with the slower bus rate yet keep the fast
internal core fed.
Chuck Moore also has some newer designs. F21 and P21, for instance.
These are 21-bit machines with (IIRC) a 20-bit external bus. Each
opcode is five bits, so (again) he's fetching four instructions with
each external bus transaction.
There was a big argument on comp.arch recently about just how hard it
is to go superscalar on a stack machine. IIRC, a Unisys A series
engineer was heavily involved in that discussion. Perhaps interested
folks can dredge it up using http://www.dejanews.com/
. I don't recall
whether there was a conclusion to the argument (is there ever a conclusion
on usenet?); a lot of the discussion was over my head.