Delay Line Memory (Was: Australian ex-DEC Director has large museumin his home)

Rick Bensene wrote: I've done a fairly detailed RE of the memory organisation of a couple of delay-line-based calculators. To throw in some more numbers to Rick's explanation, using the Monroe 925 NIXIE desktop calculator (torsion-mode delay-line) from 1970 as an example: The delay line provides for 317.5 bits of storage, across a delay of 635 uS. It is 5 ft, 14 inches (1.88 m) in length. Bits are injected into the line as 0.5 uS pulses within a 'bit slot' of 2 uS (500 KHz bit rate). Translating these values to length shows the bit pulse to occupy 0.058 inches (1.5 mm) in a slot 0.23 inches (6 mm) long, or a bit density of 51 bits/ft (169 bits/m). Calculating the propagation velocity gives 9700 ft/S (2960 m/S) or 6600 mph (10,700 Km/H). Another point, I expect, about shock sensitivity (particularly for the torsion-mode lines, not as applicable to compression-mode), is that external shocks are generally going to produce 'common-mode' vibrations in the delay elements, and so are not going to be picked up by the differential-mode transducers.