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

Brent Hilpert hilpert at
Wed Dec 3 13:23:08 CST 2008

Rick Bensene wrote:
> Göran Axelsson wrote:
> > > Slideshow: <>
> > Picture 41 shows a similar device. It was an ultrasonic
> > delay line. How much could be stored in such a memory?

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.

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