Harvard Mark I

By the late 1930s punched-card machine techniques had become so well established and reliable that Howard Aiken, in collaboration with engineers at IBM, undertook construction of a large automatic digital computer based on standard IBM electromechanical parts. Aiken's machine, called the Harvard Mark I, handled 23-decimal-place numbers (words) and could perform all four arithmetic operations; moreover, it had special built-in programs, or subroutines, to handle logarithms and trigonometric functions. The Mark I was originally controlled from pre-punched paper tape without provision for reversal, so that automatic "transfer of control" instructions could not be programmed. Output was by card punch and electric typewriter. Although the Mark I used IBM rotating counter wheels as key components in addition to electromagnetic relays, the machine was classified as a relay computer. It was slow, requiring 3 to 5 seconds for a multiplication, but it was fully automatic and could complete long computations without human intervention. The Harvard Mark I was the first of a series of computers designed and built under Aiken's direction.