At the end of the 1940's Booth turned his mind to electronic machines, redesigning the ARC2 as the SEC (Simple Electronic Computer), which was then built by a graduate student Norman Kitz for his 1951 MSc (Eng) dissertation.
Norman Kitz in 1948, working on the SEC
Booth's next design was for the on to the APE(X)C All-purpose Electronic (X) Computer, where X could be replaced by the name of any sponsor who came up with the money to build one! The first was the British Rayon Research Association and so the APE(Rayon) Computer was built. The Birkbeck College Annual Report of 1951/52 records:
“The APEXC calculator operated successfully for the first time on 2nd May 1952”
The APE(X)C used a redesigned magnetic drum built by Wharf Engineering, the company formed by Booth and his father. This company produced magnetic drums for use by the new computer industry and many were exported to the USA. The first model used 415 valves and was huge.
Apart from the APE(R)C there were several one-off computers in the series, including the one used by Birkbeck College and another by University College, London. The APE(N)C was commissioned by the Norwegian Board of Mathematical Machines and went to Oslo and the APE(H)C was commissioned by the British Tabulating Machine Company, which sold Hollerith punch card equipment. The APE(X)C design used punched card technology for its input/output and the BTC was quick to recognize that the electronic computer represented a business opportunity
HEC - First UK mass produced computer
The original APE(X)C was built in a barn in Fenny Compton, Warwickshire where Booth's father lived. In 1951 the British Tabulating Company sent a three-man team, led by Dr Raymond Bird, there to copy the circuitry of the machine in order to create what would become the Hollerith Electronic Computer (HEC) and would be the first British computers to go into mass production,
In just a few days Bird’s team had copied Andrew Booth’s circuitry and back at BTM’s factory at Letchworth they added extra I/O interfaces getting the pre-production HEC1 working by the end of 1951.
BTM management decreed that the HEC would go to the Business Efficiency Exhibition in October 1953 and so a new machine, HEC2, was built in a smart metal cabinet suitable for public display. This was probably the first time that a computer had gone on public display in Britain and a noughts and crosses game served as a demonstration of the potential power of computers.
Dr Bird with the HEC2 at the Business Efficiency Exhibition 1953
Bird realised that it was essential to manufacture a machine that was operationally compatible with BTM’s punch card equipment and at a price that was in line with existing pre-computing technologies.This led to the first production model, the HEC2M, of which eight were sold mainly for technical applications.
The successor was the HEC4 which was a commercial data processing machine. Over 70 were sold in the UK and abroad, making it the UK’s best selling computer by volume at the end of the 1950s. After BTM merged with its competitor Powers SAMAS to form ICT, the HEC4 became the ICT 1200 range.
The original HEC prototype was kept in store by Birmingham Museums Collection Centre until 2016 when it went on public display at The National Museum of Computing (TNMOC) on Bletchley Park.
BTC had offered to set up a chair in Computer Engineering at Birkbeck for Booth in order to reward him but the then Chancellor and others caused the proposal to come to nothing. In disgust Booth decided to "depart from the hive of socialist mediocrity".
Within a few days he had offers of chairs from the US, Canada and New Zealand. He chose Canada and became Professor at the Western Reserve University. Booth claims to have made the right choice and certainly did a lot for engineering education in Canada - but you can't help think that this was something of a loss to the UK computer industry.
He did continue designing computers. The M3 was built at Saskatchewan University with the help of a graduate student and he worked from 1965 for ten years providing computing resources for the university. From 1972–1978 he served as President of Lakehead University in Ontario. He remained in Canada until his death in 2009 at the age of 91.
He seems never to have forgotten his own strange route through the education system and saw it as something that should be reproduced. In 1972 he started a "bright kids" program in Ontario which allowed almost anyone to take university level courses and have them credited against a degree when they finally got round to it.
His own children were among the first to benefit. Both of them started studying at 12 and graduated when they were 16 with first class honours. He felt very strongly that people should be allowed to progress at their own rate and regarded the comprehensive education revolution going on in the UK as being an attempt to bring everyone down to the lowest common level. His only overtly political achievement was to be the only University President to be listed as an Anarchist in Who's Who.
As well as designing small computers and the magnetic storage drum Booth is also responsible for "Booth's Multiplier Algorithm" which is a sneaky method for multiplying two binary numbers together and is still used in today's computing devices such as smartphones.
In those early days how to perform arithmetic was a problem and they didn't have the IEEE standard for floating point calculation to consult. Multiplying two binary numbers together is fairly easy in that it can be done using nothing but shifts and adds.
Each shift multiplies the multiplicand by two and the adds accumulate the final result. You add the multiplicand to the partial product if the multiplier bit is 1 and do nothing if it is a 0.
However this simple procedure only works for positive numbers. Negative numbers are generally represented by two's complement notation. That is -X is represented in binary as the positive number 2^n-X. This automatically gives you the correct answer when you do additions and subtractions but when you multiple a pair of two's complement numbers one positive and the other negative the answer is wrong and a correction factor has to be added.
The correction factor depends on the pattern of positive and negative values. Booth came up with a simplified and more regular algorithm for working out a signed multiplication. The algorithm is:
If the multiplier bit is a 1 and the next lower order bit is a 0 subtract the multiplicand from the partial product.
If the multiplier bit is 0 and the next lower order bit is a 1 add the multiplicand to the partial product.
If the multiplier bit is the same as the next lower bit then do nothing.
You can see that this is very simple and should be easy to implement in hardware - but can you see how or why it works?
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