What is MVS (Multiple Virtual Storage)?
MVS (Multiple Virtual Storage) is an OS from IBM that continues to run on many of IBM's mainframe and large servers. MVS is said to be the OS that keeps the world going. The same could be said of its successor systems, OS/390 and z/OS.
The payroll, accounts receivable, transaction processing, database management and other programs critical to the world's largest businesses are usually run on an MVS or successor system. Although MVS has often been seen as a monolithic, centrally-controlled information system, IBM has repositioned it (and successor systems) as a "large server" in a network-oriented distributed environment, using a 3-tier application model.
The evolution of MVS to OS/390 and z/OS
The follow-on version of MVS, OS/390, no longer included the "MVS" in its name. However, the term "MVS" will continue to be used for some time because MVS represents a certain epoch and culture in the history of computing and many older MVS systems are still in operation.
Since OS/390 also comes with UNIX user and programming interfaces built in, it can be used as both an MVS system and a UNIX system at the same time. A more recent evolution of MVS is z/OS, an OS for IBM's zSeries mainframes. MVS systems run older applications developed using COBOL and, for transaction programs, CICS. Older application programs written in PL/I and FORTRAN are still running. Older applications use the Virtual Storage Access Method access method for file management and Virtual Telecommunications Access Method for telecommunication with users. The most common program environment today uses the C and C++ languages. DB2 is IBM's primary relational database management system. Java applications can be developed and run under OS/390's UNIX environment.
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 OS 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. Throughout this evolution, application programs written for any OS have always been able to run in any of the later OSes -- also known as forward compatibility.
An MVS system has a set of basic and optional products. Customers can choose the set of functions they need. The main user interface in MVS systems is Time Sharing Option. The Interactive System Productivity Facility is a set of menus for compiling and managing programs and for configuring the system. The main work management system is either Job Entry Subsystem 2 or 3 (JES2 or JES3). Storage management is performed by the Distributed File Storage Management Subsystem. MVS is more complex and requires much more education and experience to operate than smaller server and personal computer OSes.
The Virtual Storage in MVS refers to the use of virtual memory in the OS. Virtual storage or memory enables a program to have access to the maximum amount of memory in a system even though this memory is shared among more than one application program. The OS translates the program's virtual address into the real physical memory address where the data is located. The Multiple in MVS indicates that a separate virtual memory is maintained for each of multiple task partitions.
Other IBM OSes for their larger computers include or have included: the Transaction Processing Facility -- used in some major airline reservation systems -- and VM, an OS designed to serve many interactive users at the same time.
