From the book "Computers: The Life Story of a Technology" (Eric G. Swedin and David L. Ferro, 1997): "The Atlas pioneered two important technologies: virtual memory and some aspects of time sharing. The Atlas was designed to use a memory space of up to a million words, with each word 48 bits long. No one could afford to put that much magnetic core memory in a machine, so the Atlas had actually core memory of only 16,000 words. A drum provided 96,000 more words. The operating system of the Atlas swapped memory from its magnetic core memory to the drum and back as needed in the form of pages, providing the illusion of more memory via this virtual memory scheme. The Atlas also was designed to be a time-sharing computer so that more than one program at a time could be run. To implement this time-sharing, the idea of extracode was developed, which is similar to what are now called system interrupts. These two ideas were adopted in all later operating systems of any sophistication."
* From the University of Manchester: @ and @
* From Atlas Computer Laboratory at Chilton: @ and @
* Timeline: @* From BBC: @