Add a Comment to this Note (list members only)
Dead medium: Dead memory systems
From: From: (Bradley O'Neill)
Source(s): A History of Computing Technology by Michael R. Williams; Prentice-Hall, 1985. LOC#QA71.W66 1985

pages 304-305


"The idea of thermal memory was tried by A.D. Booth, who, through the lack of other suitable material being available in Britain after the Second World War, was forced to experiment with almost every physical property of matter in order to construct a working memory. The device was never put into production because of the inherent unreliability of the system.

"Booth's thermal memory consisted of a small drum whose chalk surface was capable of being heated by a series of small wires. These wires would locally heat a small portion of the surface of the drum and, as the drum rotated, these heated spots would pass in front of a series of heat detectors. When a hot spot was detected, it was immediately recycled back to the writing mechanism which would copy it onto a clean (cool) part of the drum. The back of the drum was cooled (erased) by a small fan so that, by the time the drum had rotated to a bring the same area under the heating wires again, a fresh surface was available to receive the recycled information."


Built by A.D. Booth in post-WWII, mechanical memory "(...)consisted of a series of rotating disks, each of which contained a tiny pin which was allowed to slide back and forth through the hole, and as the disk rotated, a solenoid was used to push the pins so that they protruded from one side of the disk or the other. A small brush made electrical contact with those pins which were sticking out of one edge of the disk. It was this brush which enabled it to read the binary number stored by the pin positions.

"By putting a number of such disks together on one shaft, it was possible to produce either a serial storage unit (where one number is stored on each disk and the readout is done bit by bit as the disk rotates) or a parallel storage unit (where one number is stored on the corresponding positions of a series of disks and the readout of all the bits of a number takes place at the same instant)."

(((Booth constructed a 'disk-pin memory device', which looks like a small typewriter. About 20 reading heads are lined up along the spool, which houses the rotating disks. Booth's ARC computer used this technology at one point in its early development.)

pages 308-311


The first reliable memory system.. Utilized in the following computers:


"The basic concept behind the device was to attempt to delay a series of pulses, representing a binary number, for a few milliseconds which, although a very short time, was a relatively long period as compared to the electronic cycle time of the machine. After they had been delayed for a short time, the pulses would be fed back into the delay system to again store them for a further short period. Repeated short delays would add up to a long-term storage."

"The mercury delay-line was developed by William Shockley of Bell Labs and was improved upon by J. Presper Eckert, one of the people who designed and built ENIAC....

"(T)he mechanism would take a series of electrical pulses and convert them into sound waves by the use of a piezoelectric quartz crystal. The sound waves would then make their way, relatively slowly, down the mercury-filled tube. At the far end of the tube, the sound waves would be detected by another quartz crystal and the pulses, amplified and reshaped, would then be fed back into the front of the delay again."

(((Various problems including computer temperature, modulation/demodulation electronics, and delay time ultimately doomed this memory format. In the 1950s, advances led to the magnetostrictive delay, extinct by the 1970s.)))


4. Electrostatic storage (early CRT based systems) 5. Rotating Magnetic Memory (used in proto-disk drives, as in the 'Mail-a-Voice' recording machine) 6. Static Magnetic Memory (magnetic cores)