The system design of a general-purpose digital computer, CIRRUS, is described. An extensive order code with reasonable order execution times has been achieved at relatively low cost. Comprehensive multiprogram operation is provided. These facilities have been produced largely with microprogramming. The basic hardware is comprised of general purpose registers, a half-word arithmetic unit and two stores, all of which may be inter-connected with considerable flexibility. A substantial contribution to economy has been made by the use of a prewired ``read-only'' store of large capacity for encoding microprograms.