Don't know much about the Harvard machine but I can sort of imagine what a Zuse would sound like from seeing models and info at the Deutsches Museum. A somewhat similar comparable thing I recall really well is hearing an old relay/vacuum tube (valve) numerical position controller operate. The General Electric Century Mark II NC controls were a mid-1950's design. We had two of them, each running a large Burgmaster NC drill in our machine shop. This was from 1978 to 1983 and I was responsible for troubleshooting those danged tempermental things. They were tired, old, raggy hand-me-downs for B&L's Scientific Optical and Professional Products divisions. Paper tape was read by a Friden reader which was not all that quiet. As each digit was read off the tape, a corresponding 10-position stepper switch would step to that digit. More noise. After the last digit of the possible 12 was stepped there was some clatter from the dozens of hermetically sealed relays in the relay logic area and the error voltage was set for each axis. The steppers would then immediately reset to zero or home position. That was a bunch of noise. The servo drive amplifiers would move the table to position. Relatively quiet. The drilling, boring or tapping function would be performed. Some noise depending upon spindle speed, feed rate and material. Then the cycle would start once again for the next location on the workpiece. For a very complex part or group of parts in a holding fixture and if only simple holes were being drilled, *and* if the NC control was working well, each cycle could be only 5 to 10 seconds long. If the number of holes being drilled was, say, 30 to 50 or so one could imagine the sweet buzz-buzz-bizz-bizz-buzz, clatter, clickety-click-clack, bzzzzz sounds of an electromechanical NC positioning system at work going on for significant periods :) So, this experience helps me imagine a little of what the old relay computers may have sounded like at certain times doing certain operations. I spent *many* hours troubleshooting these NC units while in that noisy machine shop trying to hear certain relays faintly click at just the right time while holding scope probes in both hands (looking at other relay outputs or servo signals, etc.) and operating the 'Start' button with my foot (yes, it all looked strange). Relay races because of faulty contacts were a common problem. The design relied upon very close timing of relay contact closures or openings. The relays could not be opened to check plus they were getting extremely expensive by 1982 (approx $100 each.) Other than a scope, using the right cuss words occasionally helped too. Only one other person at that time knew those controls as well and that was the GE Field Service Engineer for the Mark II's who took care of most of the Eastern USA *just* on those controls. I still have the printsets somewhere around I think. In a quiet shop with the control cabinet doors wide open, even carrying on a normal conversation next to the controls was sometimes hard depending upon the hearing ability of the person I was talking with. The Mark II's sounded like only a hundred women knitting plus a small telephone Central Office switch and a Teletype. Regards, Chris -- -- Christian Fandt, Electronic/Electrical Historian Jamestown, NY USA cfandt(a)netsync.net Member of Antique Wireless Association URL: http://www.ggw.org/awa