Atlas was a mainframe computer built by a consortium of the University of Manchester, Ferranti, and Plessey. It was, for two years in the early 1960s, the most powerful computer in the world, before the advnt of the IBM 7030 Stretch. It is notable for being the first computer to have virtual memory (called 'one-level store').
Its addresses were 24 bits, in 48-bit instructions; the address space allocated to main memory was 20 bits. Its main memory initially consisted of 16K 48-bit words of core memory, which was allied with 96K words of drum in four drives.
After the prototype at Manchester was completed, two more were built by Ferranti, for users in the UK.
- Raúl Rojas, Ulf Hashagen, The First Computers: History and Architectures; Frank H. Sumner, "The Atlas Computer"