Completely and utterly bonkers
But I hope he manages to complete it and find a home for it because it'll be a wonderful achievement.
I'm assuming it'll go abroad because that's where most great British technology ends up...
A bloke in Cambridge, UK, is building a computer processor using 14,000 individual transistors and 3,500 LEDs – all by hand, piece by piece. James Newman said his Mega Processor relies almost entirely on the hand-soldered components, and will ultimately demonstrate how data travels through and is processed in a simple CPU core …
Doesn't have to go abroad, bring it to the Museum of Computing in Swindon if they have space (it's almost abroad, I guess, from a Cambridge perspective). It may not be truly a museum piece yet, but it's undeniably a brilliant educational tool.
We have good beer, too.
If you haven't, go and look at the WEB site for the project. It's fascinating, board construction, component layout, testing, managing connections. Amazing breadth of skills the man has.
From his site:
"I spent a bit of time trying to work out how to do the 7-segment display using discrete transistors but the answer is vast. Really, really big. It would have near doubled the size of the thing and the circuitry for the display would have obscured the circuitry for the processor which would have undermined what I was trying to do. As its only for debug and not proper function I went for chips. This is definitely NOT cheating, it is just for debug. It is irritating though."
"The RAM's turning out to be quite sizable. A square inch per bit ! I'm hoping to do 64 bytes, but that translates to the best part of two square metres."
Really, I had to laugh. Sizeable? Not half it isn't.
>There are several examples of those monstrosities around.
None of which are actually functioning today. The Computer History Museum in California has a number of historic tube computers which would be a nightmare to restore to working order. Most of them used magnetic drum memories, guaranteed to be nonfunctional and almost impossible to repair. The only tube computer that is functional today is the Colossus replica at Bletchley Park, and it's not even a "general purpose" computing device.
"None of which are actually functioning today"
AFAIK the replica of the Manchester 'Baby' is around and ran in 1998. I was taught physics by a chapvwho worked on the original and had a photo of himself, stripped to the waist, working in basement surrounded by racking
The RAM's turning out to be quite sizable. A square inch per bit !
Sounds like he's using static RAM, maybe he should have tried a dynamic RAM design? With decent capacitor sizes he wouldn't have too fast a refresh cycle...
I suppose core memory would be better still, if he's into knitting!
Those wires act as huge capacitors which need to charge and discharge on each cycle to allow the signal to stabilise.
The general rule for a signal to settle on a plain old wire is something like six times longer than the speed of light along the wire. (Or two to-and-fro bounces at 0.7c)
I've often wondered what is the optimum design for a discrete-transistor computer. Minimise the transistor count, build as small as possible, and clock as fast as possible, or go for wider buses and more transistors clocking more slowly? (Of course in the early days they went for small component counts, because transistors - germanium alloy junction ones - were significantly expensive, and suffered thermal runaway at fairly low temperatures so cooling really mattered. )
"It's only 14m long. Assuming 0.7c because of the dielectric of the wires that would be 66.6ns propagation delay end-end. So you could run it under 15MHz, say 1MHz should be do-able"
Yeaaahhhh... I only know a tiny little bit about RF, so I might be talking complete rubbish here, but wouldn't there be radiation issues? I seem to remember that one of the constraints on the original IBM PC (4.77 MHz) was that pushing the clock any higher led to disproportionately high energy losses to radiation (and of course interference with your transistor radio!), and that on a printed circuit board of much less than 2 sq ft. I imagine that a 14m long assembly with lots of interconnecting cable and hand-soldered assemblies might have a slightly worse problem with that.
Take a look at a photo of an old enough computer that the CPU consisted of a large number of logic modules connected with a wire-wrapped backplane (for example Google "Images PDP-8 Backplane). You'll soon deduce that the interference problem is not insurmountable. It was not negligible, though!
The routing of wires within the backplane was a black art. Some were artificially lengthened so as to introduce deliberate signal delays. Others took non-parallel routes from A to B to reduce crosstalk - interference is by far the greatest between closely parallel wires. The general term was "random-wired". It was most definitely not a good idea for structure in the circuit schematics to be explicit in the physical arrangement of wires in the backplane.
To some degree it not just the length of the wires, but the differences in length wrt the frequency being used.
I sure hope he's keeping the length of the wires (as appropriate) the same to each (and within) similar functional banks of transistors, otherwise the differing propagation delays will be madness to try to debug. This is normally done at chip layout and PCB layout. Clocking in incorrect bits (on some lines) and not others would surely lead to a long stay at a mental institution.
Slowing down the frequency until it worked might be practical, but with a little attention to the lengths, he might find that he could run at a much higher frequency. Overclock - baby....
kHz or KHz is valid, after all, little "m" means "milli", big "M" means "mega", as kilo = 1000, it is a multiplier and can be K. But from wikipedia:
* The engineer's society, IEEE, and most other sources prefer "kHz" to "KHz." This apparently makes it less likely that users will confuse "kilo" (decimal 1,000) with the computer "K" (1,024).
I'm no fan of "coding" in schools.
Which seems to be pretty pointless for most kids.
But if we're showing the kids what is actually under the bonnet and then letting them try to make it do something there's a chance that some ( the right ones ) will be inspired to really get involved.
I seem to remember a ladybird book ( I think) with a computer made from wood and OC71 germanium transistors, and some dairy/milk Co series* of many-how to booklets that did the same sort of thing.
Where are these sort of things now...?
*can't find them on Goog - they were thin, square and white, with blue titles etc.
Awesome! I cannot approve more of this project - what a geek, utterly awesome!
Cambridge Uni: He mentions space is a problem for the final CPU, please promise this guy a room for a few months to demo the finished CPU - knowing this will surely aid his motivation.
Funding: How much is this all costing? Where do I donate some transistors?
A technology that existed in Babbage's time, but of which Babbage was unaware, is hydraulic logic. It's possible to create a bistable out of fluid (air) being pumped through an appropriately shaped cavity, and to switch it between its two stable states using pipework connected to the output of others. Logic gates are also feasible.
Anyone fancy building the world's first (?) hydraulic programmable computer?
Or even a simulation thereof, just to hear what it might sound like while it is computing.
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