My Big Gravity Powered Mechanical Computer on Display

If you think hard enough, I bet you’ll be able to remember seeing things when you were very young that just astonished you, and in some way influenced you as you got older. For me, I can still remember seeing mechanical computers like the Digi-Comp 1 (1963) and the Think-a-Tron toy (1960).


So, a couple of months ago I decided I’d make a scaled up version of a gravity powered mechanical computer. I called my device Gravi-Comp because it’s modeled after the Digi-Comp 2 (1967) that inspired so many young people in the 1960s and 70s. Gravi-Comp can add, subtract, multiply and divide where the result is up to a 7-bit (small) number. For example, it can multiply up to 7 * 15 = 105.

I work in Microsoft Research in Redmond, Washington, in “Building 99”. The building has an area called Studio99 where we display interesting items that are related to art and technology. Last week, the people who organize Studio99 put Gravi-Comp on display.


I noticed that people tended to react to Gravi-Comp in different ways. Some people barely looked at it and had little interest. But most of the people who saw it just couldn’t keep their hands off it and immediately started playing with the device to see how it worked.


Many people have made similar devices, often using Lego. But I wanted something a bit bigger so I used a laser cutter and acrylic plastic. Gravi-Comp is fairly impressive in person. It stands about 8 feet tall and weighs over 600 lbs.

My hope is that some young people will see Gravi-Comp and be just as fascinated by computers as I was many years ago.

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