IBM 1620

The IBM 1620 is a model of scientific minicomputer that was produced by IBM. It was announced on October 21, 1959, and was then marketed as an inexpensive scientific computer. After a total production of about two thousand machines, it was withdrawn on November 19, 1970. Modified versions of the 1620 were used as the CPU of the IBM 1710 and IBM 1720 Industrial Process Control Systems (making it the first digital computer considered reliable enough for real-timeprocess control of factory equipment).

Being variable-word-length decimal, as opposed to fixed-word-length pure binary, made it an especially attractive first computer to learn on; hundreds of thousands of students had their first computer experience on the IBM 1620.

Core memory cycle times were 20 microseconds for the (earlier) Model I, 10 microseconds for the Model II (about a thousand times slower than typical computer main memory in 2006). The Model II was introduced in 1962.