What Operating System did the colossus run?

The Colossus, the world's first programmable digital computer developed during World War II, did not run a conventional operating system like modern computers. Instead, it was programmed using a series of plugs and switches, with its operation governed by a specific set of instructions for cryptanalysis tasks. The machine utilized a form of binary-coded decimal and was designed to perform specific computations for breaking encrypted messages. Its programming was largely manual and tailored to the specific needs of the code-breaking efforts at Bletchley Park.