Historians disagree about how to categorize the machine pictured above. Was it the first computer? A mammoth mechanical calculator? But there is no question that the differential analyzer-shown with its inventor, MIT's Vannevar Bush-was a crucial player in the history of computing.

Bush designed the device to solve differential equations in an attempt to model the rapidly expanding power systems of the 1920s. When completed in 1931, the analyzer used electric motors to drive shafts and gears that represented each term in a complicated equation.