Zuse Z4 - Oldest Surviving Computer in the World - Lost in the archives

dwight dkelvey at hotmail.com
Fri Oct 2 08:41:13 CDT 2020

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.

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

> On Oct 1, 2020, at 1:20 PM, dwight via cctech <cctech at classiccmp.org> wrote:
> It is going to need a lot of contact cleaning.
> The one thing I like is the carry design the Zuse used. Really fast for relays but not of much use for solid state.
> Dwight

Where did you find that?  I looked through the document that was posted and I don't see that detail in it.


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