Homebrew Drum Computer architecture

John Robertson jrr at flippers.com
Thu Dec 20 10:18:19 CST 2007

Not sure if this is of any use, but back in about 1965/66 the high 
school I was going to in Toronto was building an analog computer - 
gears, pulleys, cams, shafts, etc.  I recall it being a rather largish 
machine about 6 feet long and three or so feet deep and four to five 
feet off the ground. I was not interested in it (I was 14 at the time 
and only interested in old battery radios at that time) other than 
spotting it on my first tour of the place.

The school (if anyone here lives in Toronto) was/is Upper Canada College 
(private boys school - I only lasted one year there). I have no idea if 
the project was ever finished or if it still exists, but it struck me - 
reading this thread - that someone might be interested enough to see if 
it is still buried in the bowels of the main building. I doubt it, but 
one never knows!

John :-#)#

Robert Nansel wrote:
> Thanks for all the great ideas so far!  In no particular order:
> * Delay lines:  I have a junk magnetostrictive DL on the way.  I don't 
> know if it works.
> * The idea behind using cassette heads is just to test out my logic 
> and R/W amplifiers at s-l-o-w speed.  A baby step.  The high-speed 
> stuff would come later. I do have a small lathe (a Taig), so I can 
> handle some of the machining, provided the drum is small (around 4" 
> dia x 9" long).  If I can rig a tool-post grinder I might be able to 
> do all of it.
> * As for the drum coating, it would either be plated with nickel or 
> coated with a mixture of ferric oxide and epoxy.
> Now for some more questions:
> I haven't settled on the machine architecture yet.  I was thinking a 
> smaller word size would be better because the recirculating registers 
> would have lower latency; that is, a 16-bit word would halve the word 
> time vs. a 32-bit word.  Does this make sense?
> One of the big problems with drum machines is the need to ensure 
> instructions are optimally placed on the drum.  To lighten the load a 
> bit I'm considering making it a zero-address  stack machine.  Then I 
> only have to worry about the occasional random access reads/writes.  I 
> was thinking I  would implement a data stack and a return stack, each 
> being made of short recirculating buffers to hold the top two or three 
> stack entries, with the older entries swapped to longer buffers with 
> corresponding longer access times.  Allowing for the overall insanity 
> level of this project, is this seem a sane strategy?
> -Bobby

John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9 
Call (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, VideoGames)
"Old pinballers never die, they just flip out"

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