The Colossus Rebuild Project by Tony Sale

Colossus Reborn

Early days

In the 1970s, information about Colossus began to emerge. Professor Brian Randell of Newcastle University started researching early computers, among them Colossus.
Dr Tommy Flowers and some of the other design engineers gave papers in the 1980s describing Colossus in fairly general terms.
In 1989 I joined the staff of the Science Museum of London as manager of a project to restore some early computers to working order namely a Ferranti Pegasus electronic valve computer of 1956, an Elliott 803 transistorised computer from 1962 and an original DEC PDP 8.
Although I had a basic knowledge of computer history I decided that if I were to be talking to the real pioneers of computing I had better brush up on my history. so I spent 3 months researching the first 100 computers in the world. In the course of this I found all the published papers on Colossus. Not a lot. But I and my colleague Chris Burton, who was heading up the Pegasus restoration believed it might be possible to recreate Colossus and some other early machines which had disappeared.

The start of the rebuilding of Colossus

When, in 1991, I joined the campaign to save Bletchley Park from demolition by property developers, I believed it would be possible to rebuild Colossus.

Nobody believed me.

I renewed my contacts with GCHQ and in 1993 I gathered together all the information available. This amounted to the eight 1945 wartime photographs taken of Colossus plus some fragments of circuit diagrams which some engineers had kept quite illegally, as engineers always do!

The first stage was to produce accurate machine drawings of the frames for Colossus (all the original machine drawings had been burnt in 1960). This involved three months of eyestrain poring over the photographs and using 3D projections to transfer the details to a CAD system, EasyCad running on a 486 PC.

The biggest unknown was the height of the racks. Nobody who was there could remember exactly what it was. So having used the 3D projection system to move the viewpoint in the photos to normal to the face of the racks I then scaled up from known component sizes, jack plug strips, valve holders and switches, to arrive at the rack heights. All these measurements converged on 80 inches height, so that is what has been used for the rebuild.

This page was originally created by the late Tony Sale, the original curator of the Bletchley Park Museum, and Secretary of the Bletchley Park Heritage Society.