History of IBM Mainframe Operating Systems - Before System/360

Before System/360

IBM was slow to introduce operating systems: General Motors produced General Motors OS in 1955 and GM-NAA I/O in 1956 for use on its own IBM computers; and in 1962 Burroughs Corporation released MCP and General Electric introduced GECOS, in both cases for use by their customers.

In fact the first operating systems for IBM computers were written by IBM customers who did not wish to have their very expensive machines ($2M in the mid-1950s) sitting idle while operators set up jobs manually, and so they wanted a mechanism for maintaining a queue of jobs.

The operating systems described below ran only on a few processor models and were suitable only for scientific and engineering calculations. Users with other IBM computers or other applications had to manage without operating systems. But one of IBM's smaller computers, the IBM 650, introduced a feature which later became part of OS/360: if processing was interrupted by a "random processing error" (hardware glitch), the machine could automatically resume from the last checkpoint instead of requiring the operators to restart the job manually from the beginning.