Atlas (computer)

The University of Manchester Atlas in January 1963

The Atlas Computer was a joint development between the University of Manchester, Ferranti, and Plessey. The first Atlas, installed at Manchester University and officially commissioned in 1962, was one of the world's first supercomputers, considered to be the most powerful computer in the world at that time.[1] It was said that whenever Atlas went offline half of the United Kingdom's computer capacity was lost.[2] It was a second-generation machine, using discrete germanium transistors. Two other Atlas machines were built: one for British Petroleum and the University of London, and one for the Atlas Computer Laboratory at Chilton near Oxford.

A derivative system was built by Ferranti for Cambridge University. Called the Titan, or Atlas 2, it had a different memory organisation and ran a time-sharing operating system developed by Cambridge University Computer Laboratory. Two further Atlas 2s were delivered: one to the CAD Centre in Cambridge (later called CADCentre, then AVEVA), and the other to the Atomic Weapons Research Establishment (AWRE), Aldermaston.

The University of Manchester's Atlas was decommissioned in 1971,[3] but the last was in service until 1974.[4] Parts of the Chilton Atlas are preserved by National Museums Scotland in Edinburgh; the main console itself was rediscovered in July 2014 and is at Rutherford Appleton Laboratory in Chilton, near Oxford. CADCentre's Atlas 2 was decommissioned in late 1976.


Development of MUSE—a name derived from microsecond engine—began at Manchester University in 1956. The aim was to build a computer that could operate at processing speeds approaching one microsecond per instruction, about one million instructions per second.[5] The prefix micro- (abbreviation µ) in the SI or International System of Units denotes a factor of 10−6 (one millionth).

At the end of 1958 Ferranti agreed to collaborate with Manchester University on the project, and the computer was shortly afterwards renamed Atlas, with the joint venture under the control of Tom Kilburn. The first Atlas was officially commissioned on 7 December 1962, and was considered at that time to be equivalent to four IBM 7094s[1] and nearly as fast as the IBM 7030 Stretch, then the world's fastest supercomputer.

Technical description


The machine had many innovative features but the key operating parameters were as follows (the store size relates to the Manchester installation; the others were larger):

Atlas did not use a synchronous clocking mechanism—it was an asynchronous Processor—so performance measurements were not easy but as an example:


One feature of the Atlas was "Extracode", a technique that allowed complex instructions to be implemented in software.

The uppermost ten bits of a 48-bit Atlas machine instruction denoted which operation should be performed. If the most significant bit was set to zero, this was an ordinary machine instruction executed directly by the hardware. If the uppermost bit was set to one, this was an Extracode and was implemented as a special kind of subroutine jump to a location in the fixed store (ROM), its address being determined by the other nine bits. About 250 extracodes were implemented, of the 512 possible.

Extracode mode had its own program address counter, and easy access to the instruction operands.

Extracodes were what would be called software interrupt or trap today. They were used to call mathematical procedures which would have been too inefficient to implement in hardware, for example sine, logarithm, and square root. But about half of the codes were designated as Supervisor functions, which invoked operating system procedures. Typical examples would be “Print the specified character on the specified stream” or “Read a block of 512 words from logical tape N”. Extracodes were the only means by which a program could communicate with the Supervisor. Other UK machines of the era, such as the Ferranti Orion, had similar mechanisms for calling on the services of their operating systems.


Atlas pioneered many software concepts still in common use today, including the Atlas Supervisor, "considered by many to be the first recognisable modern operating system".[6]

One of the first high level languages available on Atlas was named Atlas Autocode, which was contemporary to Algol60 and created specifically to address what Tony Brooker perceived to be some defects in that language. The Atlas did however support Algol 60, as well as Fortran and COBOL. Being a university machine it was patronised by a large number of the student population, who had access to a protected machine code development environment.

See also

Notes and references


  1. 1 2 Lavington 1998, p. 41
  2. Lavington 1998, pp. 44–45
  3. Lavington 1998, p. 43
  4. Lavington 1998, p. 44
  5. The Atlas, University of Manchester, retrieved 21 September 2010
  6. Lavington 1980, pp. 50–52


  • Edwards, Dai (Summer 2013), "Designing and Building Atlas", Resurrection: The Bulletin of the Computer Conservation Society, 62: 9–18, ISSN 0958-7403 
  • Lavington, Simon (1980), Early British Computers, Manchester University Press, ISBN 0-7190-0803-4 
  • Lavington, Simon (1998), A History of Manchester Computers (2 ed.), Swindon: The British Computer Society, ISBN 978-1-902505-01-5 

Further reading

External links

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