Pegasus was an early thermionic valve (vacuum tube) computer built by Ferranti, Ltd of Great Britain. This article is about the electronic device not an evacuated pipe used for experiments in Free-fall. Ferranti or Ferranti International plc was a major UK Electrical engineering and equipment firm known primarily for defence Electronics and See also Kingdom of Great Britain Great Britain (Breatainn Mhòr Prydain Fawr Breten Veur Graet Breetain is the larger of the two main islands
The Pegasus 1 was first delivered in 1956 and the Pegasus 2 was delivered in 1959. Ferranti sold twenty-six copies of the Pegasus 1 and twelve copies of the Pegasus 2, making it Ferranti's most popular valve (vacuum tube) computer.
Christopher Strachey recommended these design objectives:
- Optimum programming (favored by Alan Turing) was to be avoided "because it tended to become a time-wasting intellectual hobby of the programmers";
- The needs of the programmer were to be a governing factor in selecting the order code (instruction set); and
- It was to be cheap and reliable. Christopher Strachey (1916&ndash1975 was a British Computer scientist. In the history of computing optimum programming is the practice of arranging a computer program's instructions in memory so as to minimize the time the machine spends waiting for instructions Alan Mathison Turing, OBE, FRS (ˈt(jʊ(ərɪŋ (23 June 1912 &ndash 7 June 1954 was an English Mathematician An instruction set is a list of all the instructions and all their variations that a processor can execute (See also Optimum programming for further information. In the history of computing optimum programming is the practice of arranging a computer program's instructions in memory so as to minimize the time the machine spends waiting for instructions )
Pegasus had eight accumulators, seven of which could also be used as index registers. In a Computer 's central processing unit ( CPU) an accumulator is a register in which intermediate arithmetic and logic results are stored An index register in a computer's CPU is a Processor register used for modifying Operand addresses during the run of a program typically for doing vector/ (It was the first computer to allow this dual use. ) Accumulators 6 and 7 were know as p and q and were involved in multiply and divide and some double length shift instructions. In a Computer 's central processing unit ( CPU) an accumulator is a register in which intermediate arithmetic and logic results are stored It had 56 words of fast memory stored in nickel delay lines, which was supplemented by a magnetic drum holding 5120 words. In Computing, " word " is a term for the natural unit of data used by a particular computer design Genesis in radar The basic concept of the delay line originated with World War II Radar research as a system to reduce clutter from reflections from the ground Drum memory is a magnetic Data storage device and was an early form of Computer memory widely used in the 1950s and into the 1960s invented by Gustav Tauschek A word was 40 bits, of which one bit was for parity checking. A bit is a binary digit, taking a value of either 0 or 1 Binary digits are a basic unit of Information storage and communication In Mathematics, Computer science, Telecommunication, and Information theory, error detection and correction has great practical importance in Two 19-bit instructions were packed into one word and the extra bit (not counting the parity bit) could be used to indicate a breakpoint (optional stop), to assist in debugging. In Computer science, an instruction is a single operation of a processor defined by an Instruction set architecture. Error detection If an odd number of bits (including the parity bit are changed in transmission of a set of bits then parity bit will be incorrect and will thus indicate A breakpoint, in Software development, is an intentional stopping or pausing place in a program, put in place for Debugging purposes It had a relatively large instruction set. It was about the same speed as the Elliot 402 computer, which could add in 204 microseconds and multiply in 3366 microseconds. The second ( SI symbol s) sometimes abbreviated sec, is the name of a unit of Time, and is the International System of Units The Pegasus basic instruction cycle time for add/subtract/move and logical instructions was 128 microseconds. The second ( SI symbol s) sometimes abbreviated sec, is the name of a unit of Time, and is the International System of Units Multiply, divide, justify and shift instructions took a variable time to complete. Transfers to and from magnetic drum were synchronous and had to be optimised where possible. Drum memory is a magnetic Data storage device and was an early form of Computer memory widely used in the 1950s and into the 1960s invented by Gustav Tauschek The layout of blocks on the magnetic drum was interleaved to allow some processing between transfers to/from consecutive blocks. Drum memory is a magnetic Data storage device and was an early form of Computer memory widely used in the 1950s and into the 1960s invented by Gustav Tauschek
In 1956 the first Pegasus was used to calculate the stesses and strains in the tail plane of the first vertical take off aeroplane, the SR53; the results were used to check the manufacturers figures; the programmer was Anne Robson. Because of the importance of a computer it was housed in the drawing room, complete with an Adam's ceiling, of Ferranti's London office in Portland Place.
In 1957, a Pegasus computer was used to calculate 7480 digits of pi, a record at the time. IMPORTANT NOTICE Please note that Wikipedia is not a database to store the millions of digits of π please refrain from adding those to Wikipedia as it could cause technical problems
Hugh McGregor Ross was one of the people who worked on the Pegasus. Hugh McGregor Ross (born August 31, 1917 in Nairobi, Kenya) is an early pioneer in the history of British Computing.
References
- Early British Computers, by Simon Lavington, Digital Press (US) and Manchester University Press (UK), 1980, ISBN 0-932376-08-8.
- The Pegasus Story: A history of a vintage British computer, by Simon Lavington, Michigan State University Press, 2000. ISBN 1-900747-40-5.
External links
- The Industrial Era, 1955–1957
- The 1962 edition of the Pegasus Programming Manual (38 MB PDF)
- The Computer Conservation Society, who help maintain the Pegasus installation in the London Science Museum
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