An Emulator for the Ferranti Atlas 1

The Ferranti Atlas 1 was, for a brief while, reckoned to be the most powerful computer in the world. So powerful in fact that it was said that " When Atlas goes down, the computing capacity of the entire country is halved ". 50 years on it is chiefly remembered for being the machine for which the now, almost universal system of paging was invented. But it was more than that. It was a very complex machine with no less than 100 hardware instructions and a repertoire of 262 additional pseudo-instructions (Extracodes).

The object of this emulator is to allow the execution of original and newly-written Atlas programs. No attempt is made to emulate the entire machine and multiprogramming is not supported. Because in the original machine, there was virtually nothing to see while programs were being executed, the emulator seeks to demonstrate the execution of programs by giving you an interface into the system which allows you to interact with the running program in the manner of a simplified Microsoft Visual Studio. In the emulator, Windows files take the place of the peripherals, 1" tapes, cards (.editable .txt files), paper tape and the lineprinters (editable .rtf files).

Despite having been started as long ago as 2004, the emulator is still incomplete - perhaps it always will be. But it is sufficiently complete to support a reasonable program development environment.

There are three parts to the emulator -

Here is the help file which contains full instructions for running the emulator. Feel free to browse.

The emulator runs under Windows and is written in Microsoft C#.

The emulator can be downloaded in the form of a .zip file and include various required files as well as a set of ABL test programs in a separate directory. The executable is atlas.exe.

The emulator has been used to resurrect a copy of the Brooker-Morris "Compiler Compiler" a seminal software development from the 1960s used to automate (to some extent) the writing of compilers. The source of the program was recovered from 212 foolscap pages of faintly-printed source code described in more detail here.

If you try the emulator, please email me to let me know so I can keep track of who has what. Tell me how you get on and, most importantly, let me know about any problems and ideas for improvement. My email address can be found here.

Click here to download the emulator.

© Dik Leatherdale 2004-12