The IBM CP-40 was a research precursor to CP-67, which in turn was part of IBM’s then revolutionary CP[-67]/CMS. CP-40 ran multiple instances of client operating systems, particularly CMS, the Cambridge Monitor System, built as part of the same effort. CP-40/CMS production use began in January 1967. CP-40 ran on a unique, specially modified IBM System/360 Model 40. It was the first operating system which had implemented complete virtualization.