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First released in 1974, MVS was later renamed by IBM, first to MVS/XA (eXtended Architecture), next to MVS/ESA (Enterprise Systems Architecture), then to OS/390 when UNIX services were added, and finally to z/OS when 64- bit support was added on the zSeries models; but it remains fundamentally the same operating system. Programs designed and built for MVS can still run on z/OS without modification.
MVS descends from SVS (Single Virtual Storage), which in turn descends from MVT, one of the original variants of OS/360. As the first variant of OS/360, PCP (Primary Control Program), it did not support multitasking; MVT (Multitasking with a Variable number of Tasks) was an enhancement that provided that functionality. SVS added virtual storage (more commonly known outside IBM as virtual memory), with the same address space being shared by all tasks. Finally, MVS allowed different tasks to have different address spaces.
MVS originally supported 24-bit addressing; as the underlying hardware was extended it was also to progressively support 31-bit (XA and ESA) and now (as z/OS) 64-bit addressing.
The main interfaces to MVS are JCLJob Control Language (JCL is a scripting language used on IBM mainframe operating systems to instruct the Job Entry Subsystem (that is, JES2 or JES3) how to run a batch program or start a subsystem. JCL is characterized by a pair of slashes "//" that star (Job Control Language), the batch processingBatch processing is the sequential execution of a series of programs ("jobs") on a computer. The term batch originated in the days when programmers wrote code on paper forms which would be keypunched onto 80-column punch cards or paper tape. The cards or interface, and TSO (Time Sharing Option), the interactive time-sharingAlternate uses: see Timesharing Time-sharing is an approach to interactive computing in which a single computer is used to provide apparently simultaneous interactive general-purpose computing to multiple users by sharing processor time. Because early mai interface, which originally was optional but is now a standard component. ISPFISPF (Interactive System Productivity Facility) is a tool set for the IBM z/OS ( MVS, OS/390) operating system for mainframe computers. It includes a screen editor, the user interface of which was emulated by some microcomputer editors sold commercially i is an interface which allows to accomplish the same tasks as TSO but in a menu and form oriented manner.
The system is typically used in business and banking, and applications are often written in COBOLCOBOL is a second-generation programming language. Its name is an acronym, for CO mmon B usiness O riented L anguage defining its primary domain in business, finance, and administrative systems for companies and governments. Prehistory and specification C. COBOL programs were traditionally used with transaction processing systems like IMSIMS began as a hierarchical database designed by IBM for Rockwell for the Apollo program. It was used to track the bill of materials for the Saturn V. IMS is still running thirty five years later and over time has seen some interesting developments as IBM and CICSCICS (Customer Information Control System is a transaction server that runs on IBM Mainframe systems under MVS, z/OS or DOS/VSE. CICS is a transaction processing system, which can be called online transaction processing. CICS is needed with operating syst. For a program running in CICS special EXEC CICS statements are inserted in the COBOL source code. A preprocessor (translator) replaces those EXEC CICS statements with the appropriate COBOL code to call CICS (compare with SQL used to call DB2) before the program is compiled. Applications can also be written in other languages such as C, C++, Java, Assembler, Fortran, BASIC, RPG, and REXX. Language support is packaged as a component called "Language Environment" or "LE".
MVS systems are traditionally accessed by 3270 terminals, or by PCs running 3270 emulators; many mainframe applications these days have custom web or Windows interfaces. The z/OS operating system has built-in support for TCP/IP. System management, done in the past with a 3270 terminal, is now done through the Hardware Management Console (HMC). Operator consoles are provided through 2074 emulators. So you are unlikely to see any S/390 or zSeries processor with a real 3270 connected to it. The z/OS operating system also has native support to execute POSIX applications.
Files are called "data sets" in MVS; these files are organized in "catalogs". The native encoding scheme of MVS is Big Endian EBCDIC but MVS provides services to perform translation and support of ASCII, Little Endian, and Unicode.
One instance of an MVS operating system is called a "Logical Partition" or "LPAR"". Multiple LPARs can be organized and collectively administered in a structure called a "Systems Complex" or "Sysplex". The LPARs interoperate through a software component called a "Cross-system Coupling Facility" or "XCF" and a hardware component called a "Hardware Coupling Facility" or "CF". Multiple Sysplexes can be joined via standard network protocols such as TCP/IP or IBM's proprietary Systems Network Architecture (SNA). The Sysplex was introduced in September, 1990. An LPAR can also be initialized to run other operating systems, such as Linux, VSE, TPF, or VM.
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