The Atlas Computer of the University of Manchester became operational in 1962, having been a joint development between the University, Ferranti and Plessey. It was said at the time that whenever it went offline half of the UK computer capacity was lost.

Two other Atlas machines were built: one for British Petroleum (BP) and the University of London and one for the Atlas Computer Laboratory at Chilton near Oxford. A derivative system was built by Ferranti for Cambridge University, called the Titan, which had a different memory organisation, and ran a time-sharing operating system developed by Cambridge Computer Laboratory.

The University of Manchester's Atlas system was eventually decommissioned in 1971.

Technical description

Hardware

The machine had many innovative features but the key operating parameters were:

• 48-bit word size
• 24-bit address space
• 16K words of core store (equivalent to 96 KB), featuring interleaving of odd/even addresses
• 96K words of drum store (eqv. to 576 KB), split across four drums but integrated with the core store using virtual memory and paging techniques
• Capability for the addition of (for the time) sophisticated new peripherals such as magnetic tape
• Addressing of peripherals through Vstore addresses and extracode routines

It did not use a synchronous clocking mechanism so performance measurements were not easy but as an example:

• Fixed-point register add — 1.59 microseconds
• Floating-point add, no modification — 1.61 microseconds
• Floating-point add, double modify — 2.61 microseconds
• Floating-point multiply, double modify — 4.97 microseconds

Software

A unique Supervisor software system managed the computer's processing time (as such it qualifies in modern terminology as an advanced job scheduler, or a simple operating system).

One of the first high level languages available on Atlas was named Atlas Autocode, which was an early forerunner to Algol. The Atlas also supported Algol 60, Fortran and COBOL. Being a university machine it was patronised by a large number of the student population who even had access to a protected machine code development environment.