[TUHS] core

[Nelson H. F. Beebe]

Tim Bradshaw <tfb at tfeb.org> commented on a paper by Tommy Flowers on
the design of the Colossus: here is the reference:

	Thomas H. Flowers, The Design of Colossus, Annals of the
	History of Computing 5(3) 239--253 July/August 1983
	https://doi.org/10.1109/MAHC.1983.10079

Notice that it appeared in the Annnals..., not the successor journal
IEEE Annals....

There is a one-column obituary of Tommy Flowers at

	http://doi.ieeecomputersociety.org/10.1109/MC.1998.10137

Last night, I finished reading this recent book:

	Thomas Haigh and Mark (Peter Mark) Priestley and Crispin Rope
	ENIAC in action: making and remaking the modern computer
	MIT Press 2016
	ISBN 0-262-03398-4
	https://doi.org/10.7551/mitpress/9780262033985.001.0001

It has extensive commentary about the ENIAC at the Moore School of
Engineering at the University of Pennsylvania in Philadelphia, PA.  Its
construction began in 1943, with a major instruction set redesign in
1948, and was shutdown permanently on 2 October 1955 at 23:45.

The book notes that poor reliability of vacuum tubes and thousands of
soldered connections was a huge problem, and in the early years, only
about 1 hour out of 24 was devoted to useful runs; the rest of the
time was used for debuggin, problem setup (which required wiring
plugboards), testing, and troubleshooting.  Even so, runs generally
had to be repeated to verify that the same answers could be obtained:
often, they differed.

The book also reports that reliability was helped by never turning off
power: tubes were more susceptible to failure when power was restored.

The book reports that reliability of the ENIAC improved significantly
when on 28 April 1948, Nick Metropolis (co-inventor of the famous
Monte Carlo method) had the clock rate reduced from 100kHz to 60kHz.
It was only several years later that, with vacuum tube manufacturing
improvements, the clock rate was eventually moved back to 100Khz.

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