MVS

MVS ( Multiple Virtual Storage ) was the most common operating system on IBM mainframes System/370 ( S/370 ) and System/390 ( S/390 ).

Past and present

MVS is a descendant of OS/360. With the introduction of the S/370 was first OS/VS1 (or OS / VS MFT Multiprogramming with a Fixed number of Tasks, similar to DOS / VS or DOS / VSE and the further developments to VSE / ESA) delivered, which until was further developed in the 1980s, parallel to its subsequent detachment OS/VS2. Release 1 of OS/VS2 supported a single virtual address space (SVS - Single Virtual Storage - and also had the designation OS / VS MVT, multiprogramming with a variable number of tasks). Release 2 OS/VS2 was released in July 1974. His full name was OS/VS2 MVS Release 2

Also the official name of the system changed - the passage of time was - mostly associated with the change of hardware architecture. So the change was after S/370XA the S/370 architecture ( eXtended Architecture - 31-bit instead of 24 -bit addressing ) the name of the operating system in MVS / XA renamed. With the introduction of the S/390 hardware (extension of the 31 -bit addressing to data spaces, Hiperspaces, expanded storage) was the name then MVS / ESA ( MVS / Enterprise Systems Architecture).

MVS included only the pure operating system and was able without any further product licenses hardly be used. Data centers had to to operate a variety of other program products of IBM or alternative providers to license. Mid-1990s, IBM changed the licensing policy and the product name of MVS OS/390 - were herein is a host of almost all required program products (such as ISPF ) included. With the release of the z / Architecture ( 64 -bit addressing ), the system was again renamed and is now called z / OS.

In colloquial usage of the mainframe specialists MVS is still in use today.

Special

MVS introduced the multiple virtual storage model. The individual applications run in address spaces and do not see the memory of other applications.

MVS was tailored to the processor architecture of the S/370. It initially supported the 24 -bit addressing, which allowed address space of 16 megabytes. Than did the hardware 31 -bit addressing is possible, this has been supported by the MVS / XA. A further step was MVS / ESA, which has made it possible to use expanded memory (called Hiperspaces ).

The user interface of the MVS are essentially the same as those of the z / OS, but without the Unix System Services. In addition to the operator console commands are the

• JCL (Job Control Language ) for batch processing and Started Tasks ( System Services )
• TSO ( Time Sharing Option ). TSO is usually used with ISPF.

The typical online applications under MVS running under IMS or CICS and based on IBM 3270 terminals. From 1983 DB2 already stood as a database.

The file system was taken over by OS/360. In addition to there existing file types (sequential, partitioned, directly and index- sequential) VSAM has been introduced. The individual files are called datasets. As EBCDIC character encoding is used instead of the usual ASCII.

Development

The further evolution of the z / OS Parallel Sysplex brought, Unix System Services, 64 -bit addressing and further improvements, where emphasis was placed on compatibility. On systems running z / OS, it is quite possible to simultaneously be modern Java web applications running alongside COBOL programs that have already been compiled in the 1960s.

Versions

Emulations

It is possible to operate the now freely available MVS up to and including version 3.8 on a Windows or Linux computer with the emulator Hercules. Newer versions are not available for this purpose.