APEXC facts for kids
The APE(X)C series was a group of early computers. They were designed by Andrew Donald Booth at Birkbeck College in London during the early 1950s. The name APE(X)C stands for All Purpose Electronic (X) Computer. The 'X' might have stood for "X-company," according to Booth.
One computer in the series was also called the All Purpose Electronic X-Ray Computer. This machine was located at Birkbeck College. The British Rayon Research Association helped fund the work on these computers.
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Why These Computers Were Built
Starting in 1943, Andrew Booth was studying crystal structures. He used a method called X-ray diffraction. This method uses X-rays to figure out how atoms are arranged in crystals. The calculations needed for this were very long and boring to do by hand. So, Booth wanted to automate the process. He first made an analog computer to help with these calculations.
In 1947, Booth and his future wife, Kathleen Britten, visited John von Neumann's team. This team was leading the way in computer research at the time.
Early Computers: ARC and SEC
Before the APE(X)C series, Booth designed other computers. One was an electromechanical computer called the ARC. This was built between 1947 and 1948.
Later, they built an experimental electronic computer. It was named SEC, which stood for Simple Electronic Computer. This was designed around 1948-1949. These early machines led to the more advanced APE(X)C series. Kathleen Booth was the person who programmed these computers.
The APE(X)C Computer Family
The APE(X)C series included several different machines. Each one had a slightly different name and purpose:
- APE(X)C: This computer was at Birkbeck College in London. It first ran in May 1952 and was ready for use by late 1953.
- APE(N)C: This one was in Oslo, Norway. The 'N' likely stood for 'Norway'. It was also known as NUSSE.
- APE(H)C: This machine was for the British Tabulating Machine Company. It's not clear what 'H' meant, but it might have been for 'Hollerith'.
- APE(R)C: This computer was for the British Rayon Research Association. The 'R' stood for 'Rayon'. It was ready to use in June 1952.
- UCC: This machine was at University College, London. It started operating around January 1956.
- MAC or MAGIC (Magnetic Automatic Calculator): This computer was built by Wharf Engineering Laboratories and started in February 1955.
- The HEC (Hollerith Electronic Computer): This was a commercial computer built by the British Tabulating Machine Company. It was later known as the ICT200 series. There were different versions like HEC 1, HEC 2, HEC 2M, and HEC 4.
Most of these computers were unique, meaning only one of each was built. However, the HEC (and possibly MAC) were commercial machines. About 150 HEC computers were sold, which was a lot for that time.
The computers were similar in design but had small differences. For example, the APEHC used punched cards for input and output. The APEXC, APERC, and APENC used teletype machines. These had a keyboard and a printer, plus a paper tape reader and puncher. The UCC had more storage (8,000 words) compared to others (1,000 words). The MAC used newer parts called germanium diodes instead of many vacuum tubes.
Computers from BTM
In March 1951, a team from the British Tabulating Machine Company (BTM) visited Andrew Booth's workshop. They used his designs to create their own computer, the Hollerith Electronic Computer 1 (HEC 1). This was done before the end of 1951. The HEC 1 was a direct copy of Booth's circuits, with added ways to input and output data.
The HEC 2 was an improved HEC 1 with a nicer metal case. It was shown at the Business Efficiency Exhibition in 1953. A slightly changed version, the HEC2M, was sold, with 8 units purchased. The HEC2M was then replaced by the HEC4. Around 100 HEC4 computers were sold in the late 1950s.
The HEC computers used standard punched cards. The HEC 4 also had a printer. It could do more complex math, like division, and had more memory locations than the APEXC.
How the APEXC Worked
The APEXC was a very simple machine in its design. It used 32-bit words for both instructions and data. This means each piece of information or command was 32 bits long.
The computer did not have RAM like modern computers. Instead, it used two magnetic drums to store information. These drums had 32 circular tracks, and each track could hold 32 words. The drums spun very fast, at 3750 rotations per minute. This meant the computer could process information quickly if the data was organized well. However, if the program instructions and data were spread out, it could be much slower. Today, even a small calculator is much faster.
One unusual thing about the APEXC was that it didn't have a program counter. In most computers, a program counter tells the computer which instruction to do next. But on the APEXC, each instruction itself included the address of the next instruction. This design helped the computer work as fast as possible with its drum memory.
The APEXC could only understand 15 different commands. These included basic math like addition, subtraction, and multiplication. It could also move data, make decisions (conditional branch), and handle input/output from paper tape. There was no read-only memory (ROM), so the computer didn't have a built-in starting program.
People usually operated the machine using a control panel. This panel let them start, stop, or pause the central processing unit. They could also change information in the computer's memory when it was stopped. To start the machine, an operator had to type in the address of the first instruction of the program. Most programs ended with a "stop" command. This allowed the operator to check the computer's status before starting another program.
The APEXC used two main input/output devices: a paper tape reader and a paper tape puncher. The punched tape output could be sent to a printer. Input tapes could be created by the APEXC itself or typed by hand using a special keyboard.
