Andrew D. Booth – Britain’s Other “Fourth Man” - History of Computing: Learning from the Past - page 32

designed a non-restoring binary multiplier which, with a subsequent minor modifica-
tion by a colleague, is the Booth multiplier which is still in use today.
Basically the Booth multiplier follows the usual method for long multiplication of
summing partial products. However it also uses a “trick” that to multiply by a string
of 9s it is possible to left shift an appropriate number of places and subtract the multi-
plier from the result. This approach works even better in binary where it results in a
simple rule:
Examine each pair of digits in the multiplier creating the first pair by appending a
dummy 0 at the least significant end, then
If the pair is 01, add the multiplicand
If the pair is 10, subtract the multiplicand
Otherwise, do nothing
Shift both the partial product and multiplier one
place right and examine the next pair of digits
Repeat as many times as there are digits in the
multiplier.
This was submitted for publication in August 1950 and published the following
year [9].
5 Commercial Success
Accommodation at bomb damaged Birkbeck was still at a premium throughout this
period and so Andrew Booth built his APE(R)C and probably later computers in a
barn in Fenny Compton, Warwickshire where his father lived.
It was to this barn in March 1951 that a three man team led by Dr Raymond
“Dickie” Bird from British Tabulating Machines (BTM) came to visit. BTM were the
UK's leading supplier of punch card systems and their management had decided that
they needed a small computer to improve the calculating power and flexibility of their
tabulators.
At the time that BTM joined forces with Andrew Booth there were, as already
noted, three other electronic computer projects in the UK. However, strong links had
developed between the EDSAC team at Cambridge and Lyons who were building
their LEO (Lyons Electronic Office) computer. Manchester were forging links with
Ferranti, who like NPL with Pilot Automatic Computing Engine (ACE), were build-
ing large and expensive scientific computers.
In just a few days Raymond Bird's team had copied Andrew Booth's circuitry. Re-
turning to BTM's factory at Letchworth they added extra I/O interfaces and named
the resulting computer the Hollerith Electronic Computer (HEC), see Figure 5. This
prototype computer is one of the world's earliest surviving electronic computers,
unlike so many early machines which were dismantled when no longer needed, and is
now in store in the Birmingham Museum.
BTM moved ahead rapidly getting HEC1 to work by the end of 1951. BTM man-
agement decreed that the HEC would go to the Business Efficiency Exhibition in Oc-
tober 1953 and so a new machine (HEC2) had to be built contained in a smart metal
cabinet suitable for the public to see. Eight similar machines were sold as the HEC2M
mainly for technical applications. The successor was the HEC4 which was a commer-
cial data processing machine of which over 70 were sold in the UK and abroad. At the