Colossus

A working model of COLOSSUS (1943-44), the first programmable electronic digital computer — Tommy Flowers’ valve machine that broke the German Lorenz ("Tunny") cipher at Bletchley Park. It is NOT a stored-program computer: it reads a CIPHERTEXT paper-tape LOOP at high speed, electronically regenerates the five Lorenz chi-wheel patterns, and its thyratron RING COUNTERS tally Bill Tutte’s "double delta" coincidences. When the trial chi-wheel start position is correct the counter climbs far above half the tape length, and the printer reveals the setting. Use the Controller to RUN / STOP, single-STEP one tape character at a time, jog the trial χ start, JUMP TO PEAK, or switch the Q-panel logic; or open the debugger (add ?debug) to read the wheels, the counter and the found setting as machine registers and single-step the tape. The count landscape shows the peak standing proud of the noise; once every wheel is set, the tape deciphers back to the plain message.

A working model of COLOSSUS (1943-44), the first programmable electronic digital computer — Tommy Flowers’ valve machine that broke the German Lorenz ("Tunny") cipher at Bletchley Park. It is NOT a stored-program computer: it reads a CIPHERTEXT paper-tape LOOP at high speed, electronically regenerates the five Lorenz chi-wheel patterns, and its thyratron RING COUNTERS tally Bill Tutte’s "double delta" coincidences. When the trial chi-wheel start position is correct the counter climbs far above half the tape length, and the printer reveals the setting. Use the Controller to RUN / STOP, single-STEP one tape character at a time, jog the trial χ start, JUMP TO PEAK, or switch the Q-panel logic; or open the debugger (add ?debug) to read the wheels, the counter and the found setting as machine registers and single-step the tape. The count landscape shows the peak standing proud of the noise; once every wheel is set, the tape deciphers back to the plain message.