Elliott 503

The Elliott 503 computer was a big brother to the Elliott 803 computer. I have no personal experience of the 503, as they were more powerful and hence more expensive and therefore not so many were produced. The instruction set was almost identical to that of the 803, but the arithmetic unit operated in parallel, rather than serial mode, and this gave the much enhanced speed. Programs written for the 803 could, in general, be run on the 503, but this was provided that they conformed to a list of minor restrictions. In particular, Algol or Autocode programs could run directly, or be converted to the 503 dialect using utility programmes.