History of IBM mainframe operating systems

The history of IBM mainframe operating systems is significant within the history of mainframe operating systems, because of IBM's long-standing position as the world's largest hardware supplier of mainframe computers. IBM mainframes run operating systems supplied by IBM and by third parties.

The operating systems on early IBM mainframes have seldom been very innovative, except for TSS/360 and virtual machine systems beginning with CP-67. The company's prioritization of backward compatibility has allowed users to adopt new IBM systems more quickly. IBM's current mainframe operating systems, z/OS, z/VM, z/VSE, and z/TPF, are backward compatible successors to those introduced in the 1960s.