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First released in 1974, MVS was extended by program products with new names multiple times, first to MVS/SE (MVS/System Extension), next to MVS/SP (MVS/System Product) Version 1, next to MVS/XA (MVS/eXtended Architecture), next to MVS/ESA (MVS/Enterprise Systems Architecture), next to OS/390 and finally to z/OS (when 64-bit support was added with the zSeries models). IBM added Unix support (originally called OPEN EDITION) in MVS/SP V4.
MVS is a generic name for specific products that included MVS/SP (MVS/System Product), MVS/XA (MVS/Extended Architecture), and MVS/ESA (MVS/Enterprise Systems Architecture). Historically, MVS evolved from OS/360, the operating system for the System/360, which was released in 1964. It later became the OS/370 and the System/370. OS/370 evolved into the OS/VS, OS/MFT, OS/MVT, OS/MVS, MVS/SP, MVS/XA, MVS/ESA, and finally OS/390 and then z/OS.