Univac I memory tank

dwight dkelvey at hotmail.com
Thu Mar 16 18:30:36 CDT 2017

If anyone has a Diehl Combitron or one of the NCR versions. I'd love

to have one. I used one years ago while working for UofMiami.

I used it because it could be programmed and did square root.

I can't pay what one is worth but would still love to have one.


From: cctalk <cctalk-bounces at classiccmp.org> on behalf of Christian Corti via cctalk <cctalk at classiccmp.org>
Sent: Thursday, March 16, 2017 2:22:27 AM
To: General Discussion: On-Topic and Off-Topic Posts
Subject: Re: Univac I memory tank

On Wed, 15 Mar 2017, dwight wrote:
> The Olivetti used a piece of wire for the delay line. I forget what the
> Dielh Combitron used but I know it used a two delay lines. One was for
> registers and the other was for lookup tables that loaded at turn on
> time from a metal tape ( as I recall ).

I can tell you exactly what the Diehl Combitron does; I have a running
bachelor thesis for a student who is developing an emulator and assembler
for that machine, and we have also disassembled (but not yet
understood) the firmware (contained on the metal tape) of the machine.

In fact, it uses two magnetostrictive delay lines, one is called the R
delay line containing 219 bits plus one external in a flip-flop. The other
is called the M delay line with a total of 10889+1 bits. The main clock of
the machine is 1 MHz thus a bit time (called P) is 1 µs.
The R line holds four words à 55 bits, one in the I phase P bits time, one
in the I phase /P bits time, one in the /I phase P bits time and one in
the /I phase /P bits time. The instructions are always fetched from the I
phase /P bits and executed in the /I phase.
The M line holds a total of 99 P words and 99 /P words. The phase between
P and /P changes every M cycle

During the loading phase (e.g. at power on or after a 'e1' order) the R
line is filled with the contents coming from tape and then executed.
Usually the code just transfers the other three words of the R line
somewhere into the M line and restarts the loading phase for the next
block. After loading the last block a fill instruction "jumps" to the
entry point of the firmware. The fill instruction transfers four words
from the M line to the R line.


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