On 2020-Oct-01, at 2:03 PM, Paul Koning via cctalk wrote: On 2020-Oct-01, at 2:38 PM, Eric Smith via cctalk wrote: Try a search for "zuse adder", although I haven't gone through the results to see which one provides a 'good' explanation, but it looks like there are explanations out there. If I may, and in the following I hope I'm not conflating things, as it was some years ago I looked at this stuff: The idea is that a set of relays are energized in accordance with the state of the bits of the two operands. This can occur in parallel so is fast (one relay-unit-delay). Contact logic of those relays produces the sum, carry and not-carry for each bit, and the carries are wired sequentially through the contact logic of all bits. There are no intervening relays, and no relay energization is dependant upon a preceding relay in the bit sequence. Thus the entire sum and final carry are available immediately (at electric speed) after the one relay-unit-delay. No mechanical-speed ripple carry. If you try to do this with relays in a more 'obvious' manner you end up with a mechanical ripple delay down the bits. I'm not sure how unique this is to Zuse however. The raw design presented in the Radio-Electronics/Edmund Berkeley Simon articles of 1949/50 presents this scheme, although more complex (unoptimised) in the contact logic. This is post-Zuse of course, but it's a question and investigation as to how the design may have gotten from Zuse to the US/Berkeley in those years. That is, I wonder if it's a design that was arrived at independently in multiple places, or did it all derive from Zuse. When I was figuring-out/recreating the design of 'Simon' some years ago, I optimised the RE/Simon adder design down considerably. That's written up here, in the ALU/adder section: http://madrona.ca/e/simon/imp.html The schematic there presents the idea. Some years later I ran across the Zuse design and found I was one optimisation short of Zuse (IIRC, one more contact could be optimised out and it would match the Zuse design). I've been long meaning to add the Zuse circuit into that page to present the further optimisation.

I'm sorry Paul, I didn't know you were talking about the carry circuit or I'd have replied. I don't recall where I saw the circuit described but with relay contacts, the carry was basically as fast as the sum was created. It was kind of a parallel operation. It didn't require different relay coils to actuate to pass the carry to the next relay stage. It was all just contacts for the carry to propagate. The reason I said it wasn't much use in today's circuits is that you can only series transistors to 3 or4 transistors before things slow down to much compared with driving an inverter. It has a lot to do with the non-zero resistance and the hidden charge stored between two transistors that are turned off. The worst case happens when the entire stack of transistors tries to turn on at the same time. Relay contacts themselves pass data in less than a micro second while relay opening and closing takes milliseconds. Designing with relays takes a different thinking. With NO and NC contacts, each coil can be thought of as a buffer or an inverter at the same time. Stacking contacts has almost no delay. One also needs to swap thinking positive and negative logic going through the circuit if it has any complexity, for if a coil is or isn't driven. Dwight ________________________________ From: Paul Koning <paulkoning at comcast.net> Sent: Thursday, October 1, 2020 2:03 PM To: dwight <dkelvey at hotmail.com>; General Discussion: On-Topic Posts <cctech at classiccmp.org> Cc: osi.superboard <osi.superboard at gmail.com> Subject: Re: Zuse Z4 - Oldest Surviving Computer in the World - Lost in the archives Where did you find that? I looked through the document that was posted and I don't see that detail in it. paul

On 01.10.20 23:38, Eric Smith via cctalk wrote:It is going to need a lot of contact cleaning. The circuit is described in Konrad Zuses life memories. There is an english translation available from the Springer publishing house. Zuse used it's own logic symbols, which he named "abstrakte Schaltgliedlogik", "abstract gating logic", because this logic could be applied to both, the full mecanical Z1 and the later relais machines. I found this carry logic built with transistors in a book from the early 1960. The author named it: killburn adder. It uses a chain of single transistors. You can find a demonstration of the Zuse-adder on: http://computermuseum.informatik.uni-stuttgart.de/virtuell/z1_adder.mp4 (sorry, it's in german only :-( ) Klemens