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From: rfm@sun.com (Rich McAllister)
Newsgroups: comp.arch
Subject: Re: delay lines for memory
Summary: A description of Hg acoustic delay lines
Message-ID: <94250@sun.Eng.Sun.COM>
Date: 16 Mar 89 03:34:59 GMT
References: <21976@lll-winken.LLNL.GOV>
Sender: news@sun.Eng.Sun.COM
Reply-To: rfm@sun.com (Rich McAllister)
Organization: Sun Microsystems, Inc.
Lines: 31
In-reply-to: brooks@maddog.llnl.gov

In article <21976@lll-winken.LLNL.GOV>, brooks@maddog writes: 
>Just to remind us of where we have been, does anyone who has access to a
>suitable article want to post a one page synopsis of just how these
>[mercury] delay lines worked?

Here's a shortend quote from _IBM's_Early_Computers_, by Bashe, Johnson,
Palmer, and Pugh, MIT Press, 1986, p110.  Highly recommended, especially for
people who think IBM never invents anything.

    The idea of using a mercury tank acoustic delay line for
    storage in computers had originated about [1944] at the
    University of Pennsylvania, where [Eckert and Mauchly
    were working on the EDVAC.]  Eckert had invented the
    mercury delay line [for radar applications.]  He
    recognized in the delay line a device capable of storing
    a large number of binary digits while requiring
    relatively few vacuum tubes.  His idea was to introduce
    a train of electrical pulses and gaps representing 1s
    and 0s, respectively, to a quartz-crystal piezoelectric
    transducer at the front of a mercury tube or tank and
    allow the acoustical waves generated by the transducer
    to propagate through the mercury.  At the far end the
    train of electrical signals was reconstructed by another
    piezoelectric transducer .... Each delay line could
    store hundreds of bits [!] at the cost of a few vacuum
    tube circuits and a temperature-controlled tank.

The temperature control is necessary to regulate the speed of sound in
the mercury, so the same number of bits always have the same delay.

Rich McAllister (rfm@sun.com)