Let's build Babbage's ultimate mechanical computer

The 19th-century Analytical Engine computer, complete with CPU and a memory, remained unbuilt – time to put that right, says John Graham-Cumming

IN 1837 British mathematician Charles Babbage described a mechanical computer that later became known as the Analytical Engine. Calling it a computer is no stretch: the Analytical Engine had a central processing unit and memory and would have been programmed with punched cards.

Parts of the Analytical Engine were built in the 1800s and are on display in the Science Museum in London along with a stack of punched cards. But Babbage never completed the project.

The computer was an extension of his well-known Difference Engine, which was designed to calculate tables of numbers such as logarithms.

While building a prototype of the Difference Engine No 1, Babbage realised that a more general-purpose machine was possible. While the Difference Engine could perform the same set of calculations over and over again, it couldn't examine its own results to change its calculations. A machine that can do that has the power of a modern computer.

Even though the Analytical Engine would have been mechanical and powered by steam, it would likely have been Turing-complete - that is, capable of computing any computable function. Babbage later returned to difference engines, designing a simpler and faster model referred to as No 2. But though he never built this machine either, he left complete plans which the Science Museum used to build a working model in the early 1990s.

So far no one has completed Babbage's tour de force: the first working computer. I think it is time to make amends.

Building the Difference Engine No 2 eliminated much of the doubt about Babbage's designs and showed that the machine could have been built in the 1800s. Since the Analytical Engine shares many elements with Difference Engine No 2, it too would likely have worked, but we won't know until we build one.

I have started a project to build an analytical engine, dubbed Plan 28 after one of Babbage's detailed plans. I'm aiming for £100,000 and hope to complete the project in time for the 150th anniversary of Babbage's death on 18 October 2021.

John Graham-Cumming is author of The Geek Atlas: 128 places where science and technology come alive. For more information visit plan28.org

If you would like to reuse any content from New Scientist, either in print or online, please contact the syndication department first for permission. New Scientist does not own rights to photos, but there are a variety of licensing options available for use of articles and graphics we own the copyright to.