Atlas Computer

The Manchester University Atlas Computer 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.

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

48 bit word size
24 bit address size
16K words of Core store featuring interleaving of odd/even addresses
96K words of Drum store split across 4 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
A unique Supervisor software system which managed computer processing time (job scheduler)
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

The system was eventually decommissioned in 1971. Two other Atlas machines were built: one for British Petroleum (BP) and London University and one for the Atlas Computer Laboratory at Chilton near Oxford. A derivative system was built by Ferranti for Cambridge University, called the Titan computer, which had a different memory organisation, and ran a time-sharing operating system developed by Cambridge Computer Laboratory.

What operating systems and programming languages were available on the Atlas? CPL was intended to be made available.

One of the first high level languages available on Atlas was named Atlas Autocode, which was an early forerunner to Algol. It 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.