A Colossus Mark 2 computer being operated by Dorothy Du Boisson (left) and Elsie Booker. The slanted control panel on the left was used to set the "pin" (or "cam") patterns of the Lorenz. The "bedstead" paper tape transport is on the right.
Developer	Tommy Flowers
Manufacturer	Post Office Research Station
Type	Special-purpose electronic digital programmable computer
Generation	First-generation computer
Release date	Mk 1: December 1943; Mk 2: 1 June 1944
Discontinued	8 June 1945
Units shipped	10
Media	Paper tape, teleprinter output
CPU	Custom circuits using valves and Thyratrons. A total of 1500 in each Mk 1 and 2400 in Mk 2. Also relays and stepping switches
Storage capacity	≤ 20 000 × 5-bit characters in paper tape loop
Memory	None (no RAM)
Display	Indicator lamp panel
Input	console switches, plug panels and photocells reading paper tape