The Colossus was built using thermionic valves, thyratrons, relays and stepping switches.

The Colossus Mark 1 used about 1600 valves and the Colossus Mark 2 used about 2400 valves. After the Colossus Mark 2 was in production and use the single Colossus Mark 1 was briefly shutdown and upgraded to a Colossus Mark 2. Five of the ten Colossus machines also had a device called the "gadget" that aided in a process called "rectangling", the number of additional valves added to each of these enhanced Colossus Mark 2 machines is unknown.

The Colossus was built using thermionic valves, thyratrons, relays and stepping switches.

The Colossus Mark 1 used about 1600 valves and the Colossus Mark 2 used about 2400 valves. After the Colossus Mark 2 was in production and use the single Colossus Mark 1 was briefly shutdown and upgraded to a Colossus Mark 2. Five of the ten Colossus machines also had a device called the "gadget" that aided in a process called "rectangling", the number of additional valves added to each of these enhanced Colossus Mark 2 machines is unknown.