This article is about the early British computer. The term "Manchester Mark 1" can also refer to the Avro Manchester heavy bomber in RAF service during the early stages of World War II.
Manchester Mark 1 was one of the world's first stored program computers.

The Manchester Mark 1 was one of the earliest electronic computers, developed at the University of Manchester from the Small-Scale Experimental Machine (SSEM) or "Baby", the world's first electronic stored-program computer. Work began in August 1948, and the first version was operational in April 1949. It was also called Manchester Automatic Digital Machine, or MADM. It is especially historically significant due to its pioneering inclusion of a kind of index register in its architecture, as well as being the platform on which Autocode was developed, one of the first "high-level" computer languages.

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[edit] Background

Main article: History of computing hardware

The Manchester Mark 1 was a direct development of the Small-Scale Experimental Machine (SSEM) which had been developed at the University of Manchester as a test-bed for the Williams tube, an early form of computer memory developed from a standard cathode ray tube (CRT). Development started almost immediately after the SSEM had successfully demonstrated the practicality of the Williams tube and the feasibility of the stored-program approach by running its first program in June 1948. Early electronic computers were generally programmed by being rewired, or via plugs and patch panels; there was no separate program stored in memory, as in a modern computer. It could take several days to reprogram ENIAC, for instance.[1]

Stored-program computers were also being developed by other researchers, notably the National Physical Laboratory's Pilot ACE, Cambridge University's EDSAC, and US Army's EDVAC. The SSEM and the Mark 1 differed primarily in the choice of memory device, using Williams tubes instead of mercury delay lines, which allowed random access to the machine's memory.

[edit] Development and design

The SSEM had been designed by the team of Frederic C. Williams, Tom Kilburn and Geoff Tootill. They were joined by two research students, D. B. G. Edwards and G. E. Thomas, with the aim of developing a realistic computing facility. Work began in earnest in August 1948, and the first version of the Mark 1 was operational by April 1949.[2]

Key improvements in the design were going to include a magnetic drum for loading programs into the machine's Williams tube memory, the addition of index registers and a binary multiplier built into the hardware. The word size (the fixed-sized group of bits that are handled together by the machine) was increased from 32-bits to 40, read and written as four 10-bit "short words". Instructions used a single short word, addresses two, and numeric data four.[clarification needed] Although the 10-bit instructions could hold up to 1,024 different codes, the machine only had 30 in its final version. Standard instruction time was 1,800 microseconds, but multiplication was much slower. The Ferranti Mark 1 (based on the Manchester Mark 1) had an addition time of 1,200 microseconds and a multiplication time of 2,160 microseconds.

The SSEM included two registers on its Williams tube, the accumulator (A) and program counter (C). Mark 1 added another (D), for holding one side of a multiplication, leaving B as the natural place to hold the index register. Since the system used a 20-bit address, the B-line on the tube held two address offsets. This is the earliest known implementation of such index/base registers – an important innovation in computer architecture, unknown in other machines until the emergence of second-generation computers (approximately 1955–1964). The Mark 1 included two tubes, each storing 64 rows ("double density") of 40 points, for a total of 128 words. 64 words was considered to be a single "page", so the system stored 4 pages. Freddie Williams deliberately sized the drum to store two "pages" of Williams tube data – that is, 2x32x40 = 2,560 bits – per track, and 32 tracks in total. The drum was timed to spin at the refresh rate of the Willams tubes, allowing pages to be read and written between refreshes, a task that took about 30 cycles.

The first version of the machine was running in April 1949, known as the Intermediary Version. This version was largely feature complete, but lacked input/output instructions to move data from the drum to the tubes, or from the paper tape to the drum.

The first realistic program to be run on the Mark 1 was a test of Mersenne primes, run in early April 1949. The computer ran error-free for 9 hours on the night of June 16-17, 1949. The Final Specification version was completed in October 1949, adding a second drum and various instructions to read one line of data to and from the drum to tubes and drum to paper tape. Over time the existing drums were used to store more data, typically 47 tracks.

The machine used 4,200 vacuum tubes for logic, which proved to be very unreliable. In one calculation the machine spent almost 25% of its time "down", due both to the tubes and the drums.[clarification needed] Nevertheless, the university was successful in attracting commercial users to rent time on the machine for £50 an hour.

[edit] Later developments

In October 1948, the United Kingdom Government's Chief Scientist, Sir Ben lockSpeiser witnessed a demonstration of the Mark 1 prototype, and was so impressed with what he saw that he immediately initiated a contract with Ferranti to manufacture a production version of the machine.[3]

After the Mark 1 began running, development continued in several directions. Dick Grimsdale and Doug Webb attempted to improve its reliability by using transistors instead of valves and their prototype, which first ran in November 1953, was perhaps the first transistorised computer. Their work was later picked up by Metropolitan-Vickers to create the Metrovick 950, of which seven were sold.

The main Mark 1 team, Tom Kilburn and Freddie Williams, concluded that computers would be used more in scientific roles than pure maths, and decided to start development of a new model including a floating point unit. The resulting machine, Meg, was both simpler than the Mark 1 as well as much faster for maths problems. Ferranti, who had built the Mark 1, rebuilt Meg with core memory and sold the resulting design as the Ferranti Mercury.

Among the Mark 1 team were mathematicians Conway Berners-Lee and Mary Lee Woods, who would later marry. Their son, Tim Berners-Lee, is today acknowledged as the inventor of the World Wide Web.

The UK's national weather service, the Met Office, used the Mark 1 to develop its first prototype computer programs for weather forecasting using difference equations to calculate atmospheric pressure.

[edit] References

Notes
  1. ^ Early Electronic Computers (1946–51), University of Manchester, http://www.computer50.org/mark1/contemporary.html, retrieved on 16 November 2008 
  2. ^ Lavington 1998, p. 17
  3. ^ Lavington 1998, p. 21
Bibliography
  • Lavington, Simon (1998), A History of Manchester Computers (2 ed.), Swindon: The British Computer Society, ISBN 0902505018 

[edit] Further reading

  • Lavington, Simon H. (Jul–September 1993). "Manchester Computer Architectures, 1948-1975". IEEE Annals of the History of Computing (IEEE) 15 (3): 44–54. doi:10.1109/85.222841. 

[edit] External links