High Quality Content by WIKIPEDIA articles! Operating System/Virtual Storage 1, or OS/VS1, was an IBM mainframe computer operating system designed to be run on IBM System/370 hardware. It was the successor to the System/360's operating system MFT (Multiprogramming with a Fixed number of Tasks), a variant of OS/360. OS/VS1, in comparison to its predecessor, was supporting virtual memory (then called virtual storage). OS/VS1 was generally available during the 1970s and 1980s, and it is no longer supported by IBM.