The Manchester Mark I and Atlas: A His torical Perspective In 30 years of computer design at Manchester University two systems stand out: the Mark I (developed over the period 1946-49) and the Atlas (1955-62). This paper places each computer in its his torical context and then describes the architecture and system software in present-day terminology. Several design concepts such as address-generation and store management have evolved in the progression from Mark I to Atlas. The wider impact of Manchester innovations in these and other areas is discussed, and the contemporary performance of the Mark I and Atlas is evaluated. CACM January, 1978 Lavington, S. architecture, index registers, paging, virtual storage, extra codes, compilers, operating systems, Ferranti, Manchester Mark I, Atlas, ICL 1.2 4.22 4.32 6.21 6.30 CA780102 JB March 28,1978 5:50 PM 3028 4 3028 3027 5 3028 3028 5 3028 3028 5 3028 3028 5 3028 3028 6 3028