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UNIVAC I Delay Line Memory

Computer designers in the late 1940s and early 1950s didn't ask how much memory, but simply how. An early random-access memory system used sound waves!

A cylindrical tank filled with mercury had piezoelectric quartz crystals mounted at each end. The crystals at the sending end of the tank converted electric pulses to sound waves that traveled relatively slowly to the receiving end of the tank, where the crystals there reconverted the waves to electric pulses that were then amplified, reshaped, and fed back to the sending end. Thus, values were kept in memory by circulating them in the tank.

The UNIVAC I contained seven memory tanks, each with 18 channels. A channel could circulate ten 12-character words. 100 channels were used for data, so the total memory capacity was 1,000 words. The computer randomly accessed each channel and then waited for the desired word circulating within it.

This was the high-speed memory of its day average access time was 222 microseconds.

Sources: UNIVAC I Maintenance Manual, Sperry-Rand Corporation, NY
J. Presper Eckert, Jr., et al., 'The UNIVAC System', reprinted in Computer Structures: Readings and Examples, NY: McGraw-Hill, 1971
Michael R. Williams. A History of Computing Technology, 2nd ed., Los Alamitos, CA: IEEE Computer Society Press, 1997. pp. 306-307, 362
William D. Bell, A Management Guide to Electronic Computers, NY: McGraw-Hill, 1957. pp. 74-75
UNIVAC I MAINTENANCE MANUAL

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