The Elliott 502 Computer is a high speed, asynchronous, stored program computer, specially designed for real-time applications. It is fully transistorised and incorporates ferrite magnetic core matrix stores. Basically it is a very fast general purpose computer having storage, arithmetic, input and output facilities, but in addition it has facilities for on-line operation of varying time dependence, whereby a number of programs may be run on a time-division basis.
The 502 operates on binary numbers of 20 digits (including a sign digit), in the parallel mode. Negative numbers are represented by the two's complement notation. It is a single address machine, and the function unit has built-in facilities for addition, subtraction, multiplication, division, collating, shifting, counting, and square root extraction, besides comprehensive input and output arrangements.
The store may be considered as a two-level store. It consists of a finite store of 1,024 words having a cycle time of 1.25 microsends, supplemented by a store, extendable in blocks of 8,192 words, with a cycle time of 3 microseconds. These are usually referred to as the Fast Store and the Main Store respectively. Programs may be obeyed from either store, and operate on data from either store.
The computer has four addressable registers:
| The Accumulator | (A) |
| The Auxiliary Register | (R) |
| The Modifier Register | (B) |
| The Sequence Control Register | (S) |
Any instructions may be modified by adding the contents of one of these registers, with the exception of the Auxiliary register.
The accumulator contains one of the two operands involved in all arithmetic functions.
Some typical times of operation are:
| Program and Data | Addition (microseconds) including access times | Multiplication (Microseconds) including access times |
| Fast Store | 2 | 10 |
| Main Store | 6 | 14 |
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Page created by Bill Purvis, last update 22nd November 2003
Contact me at: mailto:bill 'at' beeb.net