Meaning – The term OS/390, refers to the IBM operating system that includes and integrates functions previously provided by many IBM software products (including the MVS operating system) and

(a) is an open, secure operating system for the IBM S/390 family of enterprise servers,

(b) complies with industry standards,

(c) is the Year 2000 ready and enabled for network computing and e-business, and

(d) supports technology advances in networking server capability, parallel processing, and object-oriented programming.

An additional benefit of the OS/390 packaging concept was to improve reliability, availability, and serviceability (RAS) for the operating system, as the number of different combinations of elements that a customer could order and run was drastically reduced.

Example of usage“In December 2001 IBM extended OS/390 to include support for 64-bit zSeries processors and added various other improvements, and the result is now named z/OS. IBM ended support for the older OS/390-branded versions in late 2004.”