btm built a valve based computer called the hec (hollerith electronic computer). the first model (hec 1) was built in 1951, an example is held by the birmingham museum. btm went on to develop the hec 2, 2m and 4 models, eventually building more than 100. the machines had a 2 kilobyte drum memory and 1000 valves, and could use punched cards for input and output, or drive a printer.