History of IBM mainframe operating systems

The history of operating systems running on IBM mainframes is a notable chapter of history of mainframe operating systems, because of IBM's long-standing position as the world's largest hardware supplier of mainframe computers.

Arguably the operating systems which IBM supplied to customers for use on its early mainframes have seldom been very innovative, except for the virtual machine systems beginning with CP-67. But the company's well-known reputation for preferring proven technology has generally given potential users the confidence to adopt new IBM systems fairly quickly. IBM's current mainframe operating systems, z/OS, z/VM, z/VSE, and z/TPF, are backwards compatible successors to operating systems introduced in the 1960s, although of course they have been improved in many ways.