Here’s a rare look at the Harwell Dekatron, which is better known as the WITCH computer. At 2.5-tons, it’s “made from parts more commonly found in a telephone exchange; the mammoth machine, which fills a room, is as heavy as 20,000 iPhones but computed at speeds even humans could keep pace with.” Continue reading for a video and more information.

When it was built in 1951, this computer was a marvel of technology. Yet only a couple of decades later, the same processing power was available in something a little smaller. Pocket-sized, to be accurate. But for its time, the Harwell Dekatron was highly impressive. Capable of calculating sums with great accuracy 24 hours a day, it was based at the Atomic Energy Research Establishment in Harwell, Oxfordshire, where it was used for mathematical modelling.