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From: johnl@esegue.segue.boston.ma.us (John R. Levine)
Newsgroups: comp.arch
Subject: Re: Mercury delay lines
Message-ID: <1990Jun7.154830.3294@esegue.segue.boston.ma.us>
Date: 7 Jun 90 15:48:30 GMT
References: <3040@softway.oz>
Reply-To: johnl@esegue.segue.boston.ma.us (John R. Levine)
Organization: Segue Software, Cambridge MA
Lines: 33

In article <3040@softway.oz> adjg@softway.oz (Andrew Gollan) writes:
>I have always liked the idea of mercury delay lines, ...

>Can anyone tell me what machines had these memories?

They were popular in the 1950s.  Some of the early British machines used them.
The only commercial delay line machine I know of is the Packard Bell 250,
later the Raytheon 250, which I have actually programmed.  It was from about
1960, was the size of a large suitcase, and only drew 100 watts, less than the
console Flexowriter.  It had almost no console lights, and you did everything
from the typewriter using an octal debugger.  (Well, if you wanted to, you
could put a scope on a line or register and adjust the triggering to see the
word you wanted.)

The memory was divided into some number of lines (about six) each of a few
hundred 22 bit words.  You could execute instructions in successive locations,
but that required a full cycle of the line per instruction for an instruction
time measured in milliseconds.  It was much faster to spread your instructions
along the lines to minimize the wait.  I did most programming on big sheets of
paper spread out on the floor.  Line zero was 1/4 the normal length, so each
word had four addresses which you could use to minimize the delay.

The most peculiar think about it was the I/O addressing -- the line you
executed the I/O instruction from determined what device you used, e.g. a
write from line 5 went to the typewriter, and a write from line 6 went to the
paper tape punch.

And you thought Packard Bell just got into the computer business last year!

-- 
John R. Levine, Segue Software, POB 349, Cambridge MA 02238, +1 617 864 9650
johnl@esegue.segue.boston.ma.us, {ima|lotus|spdcc}!esegue!johnl
Marlon Brando and Doris Day were born on the same day.