Colossus was the first programmable electronic computer in the world. Interestingly, it was designed and developed for English code-breakers in WWII for decoding the cipher used by enemies. The computer helped the Allies read the encrypted messages being transmitted between the German High Command and the German army commands in the European war theater. The computer used vacuum tubes and used Boolean operations for functioning.
Tommy Flowers designed Colossus for solving a mathematical problem created by Max Newman. The design also received contributions from Alan Turing’s application of probability in cryptanalysis. The first prototype of the machine was named Colossus Mark 1. Developed in Bletchley Park, the prototype was demonstrated to be operational in December 1943.
The next version, Colossus Mark 2, was faster and came into operation in June 1944. It played an important role in the D-Day landings in Normandy. By the end of World War II, there were 10 of these computers in use. The first programmable computer used vacuum tubes, photomultipliers and thyratrons for optically reading paper tape and applying programmable logical functions to the characters.
Technically, the computer was designed for performing “wheel setting.” The technique helps determine the starting point of a series of key characters relative to the characters in the enciphered message on a paper table. It could examine only x wheels in the beginning. In order to keep the task controllable, not more than 2 bits of the stream were checked by the system during the early tests.
Colossus was the first electronic digital machine that was programmable. Compared to modern computing machines it didn’t store any programs. In order to set up new tasks, the operator needed to set up plugs and switches to bring changes to the wiring. Besides, unlike modern computing machines, the Colossus was not a general-purpose computer. It was designed specifically for the purpose of cryptanalysis, that involved application of Boolean operations and counting.