IBM mainframe

In the early years (1950-1965) IBM made many models of mainframes, many of which were incompatible with each other. It had two main lines of models: one for data processing use, and another one for scientific use. The two lines were largely incompatible. This all changed with the introduction of the System/360 in 1965. The System/360 was a single series of models, largely compatible with each other, for both commercial and scientific use. The System/360 was later succeeded by the the System/370, the System/390 and most recently the zSeries.

The primary operating systems in use today on IBM mainframes include MVS (also called OS/390 or z/OS), VM/CMS (also called z/VM), VSE, TPF, and most recently Linux. (A few systems also remain that run MUSIC/SP). Historical operating systems for the System/360 and its successors have included OS/360, MFT, MVT and SVS.

Many of the pre-System/360 mainframes also had operating systems, but they were very rudimentary by today's standards.

The System/370, System/390 and zSeries hardware can be emulated using the freely available Hercules emulator which runs under Linux and Windows.

See also: IBM minicomputers