IBM 1620

The IBM 1620 was announced by IBM on October 21, 1959, and 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After a total production of about two thousand machines, it was withdrawn on November 19, 1970.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-time process 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 – and hundreds of thousands of students had their first experiences with a computer 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.