A programmable, electromechanical calculator designed by Professor Howard Aiken. Built by IBM and installed at Harvard in 1944, the Mark I's 765,000 parts were used to string 78 adding machines together. It used paper tape for input and typewriters for output. According to Rear Admiral Grace Hopper, the Mark I sounded like a thousand knitting needles.
Decimal, Not Binary
The Mark I calculated in decimal arithmetic, rather than binary. At its dedication ceremony, Aiken asserted that the machine was the modern embodiment of Babbage's Analytical Engine, although it did not have a conditional statement (if this-do that) in its programming repertoire. Building the Mark I gave IBM experience that helped it develop its own computers a few years later. See Analytical Engine
The Mark I
Five tons and 51 feet of mechanical calculator, the Mark I could perform three calculations a second in 1944, and it could operate for hours without intervention. (Image courtesy of The Computer History Museum, www.computerhistory.org)