Hand-wired core for ROM?

Rick Bensene rickb at bensene.com
Fri Apr 10 11:14:37 CDT 2015

> Did the PDP14 (or any machine of that era) ever use hand-threaded (by
> end user) core boards as ROM?

AFAIK, there was no ferrite-based ROM made by DEC for use in their
computers.  There may have been aftermarket subsystems or boards that
were available for DEC machines that provided ferrite-ROM based storage,
and in some cases, it would make sense for some of the earlier machines,
before LSI ROM was available.      I could definitely see use for such
in canned applications such as process control or machine controls.
Once LSI ROM became available, these kinds of devices disappeared very

Not computers, but close in some cases:

The Wang 700-series (as well as later 500 and 600-series) electronic
calculators developed in the late 1960's used a ferrite ROM to store the
microcode that ran the machines.
The 700-series calculator was actually a redesign of what was intended
to be a computer, but was quickly converted to a calculator when HP
introduced the 9100A calculator, and Wang Labs had to scramble to make a
competitive machine.

The HP 9100 calculators also used a ferrite ROM for sequencing.

The Wanderer Conti (an early printing desktop electronic calculator
designed by Nixdorf) also used a core-based ROM for sequencing control.

The Mathatronics Mathatron calculators
(http://oldcalculatormuseum.com/c-math8-48m.html)  used threaded core
ROM to store key-press sequences to implement higher-level math

The lack of any other real means (other than diode matrices, or
capacitive type ROMs, which took up a lot of space and were expensive to
make) for storing relatively large amounts of read-only data made
ferrite-based ROM attractive.  Early on, the ROM in the Wang 700
calculator was strung by hand (by very patient and exacting women), but
eventually machines were built to at least semi-automate the process of
stringing the maze of wires.

Rick Bensene
The Old Calculator Museum

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