Henry Laurens

See also: MVS

Multiple Virtual Storage (MVS) is the Operating system large computers (“ Mainframe S ”) of IBM.

MVS was launched in 1974 by IBM. The goal was to provide a highly reliable system to support large environments of production. It is intended for the large machines of the manufacturer IBM (machines with technology CMOS nowadays called zSeries).

As its name wants to render comprehensible it (“Multiple Virtual Storage”), it applies the principle of the virtual memory simultaneously to treat various work to a machine including/understanding one or more Processeur S (up to 54, undoubtedly more in the years which comes).

MVS wants to be universal, and manages subsystems ready to answer requests in interactive mode (also called “dialogued”), as it is as well about “time-sharing” (TSO: the computer serves several users - data processing specialists generally - at the same time) that of “compromise”, where the end user, not inevitably data processing specialist, dialog with applications in connection with its function in the company (compromise monitors CICS, IMS). MVS remains however well adapted to the batch processing ( batch ), taken charges some by the language JCL.

Characteristics

The characteristics of system MVS are the following ones:

Multiprogramming: several users or work can be been useful simultaneously by the machine. “Simultaneously” means that, although at a moment given only one work can be treated by a processor, under the usual conditions all the users are been useful in turn so quickly that on a human scale they appear to use all at the same time the machine.

MVS fulfills as a function of multitask, finer as that of multiprogramming: a work can be made up of various tasks functioning the ones after the others or simultaneously: this last case they enter thus in competition for the use of the processors.

multi-task multiprogramming and it offer a “simultaneity” and a multiplicity of access to the processor satisfactory for all the users. They optimize also the use of the processor while reducing to the maximum its “idle periods”: when the work in progress awaits an unspecified event (in particular end of an input-output, “long” operation), the processor can give up it for another process ready to be activated.

Multiprocessing: several processors can be managed by the system (up to 2 in MVS-SP, 16 starting from MVS-XA). Thus, with a given moment, are treated by the machine as much process than of processors. This improves the total output of the system provided that the algorithm of scheduling is effective.

virtual memory: each work is seen offering a possible memory size being able to be quite higher than the memory really available. This is made possible by the fact that at a moment given a work does not have need for all the data nor of all the sections of code which compose it. The system leaves him the portions of memory which are necessary to him to this moment ( Working Set ), the remainder could be called disc constantly, or transferred on disc if they are data modified meanwhile, recoverable constantly at the request of work. The remainder of the memory is usefully occupied by the routines and data of the system or by other work ready to be treated by the processors.

Chronology

years 1960: OS/360 version OS/VS2 (MVT) is the large ancestor of MVS; appearance of CICS and IMS
years 1970: structure S/370 and virtual memory; 16 channels of i/o; addressing 24 bits (" barre" of the 16 MB)
years 1980: MVS/XA and addressing 31 bits; 256 channels of i/o; appearance of DB2 (relational DBMS)
years 1990: fiberoptic channels; Sysplex ( clustering of machines); abandonment of technology ECL and passage to the CMOS; MVS becomes OS/390, with a UNIX integrated (" USS" , UNIX System Services : they are in fact standardized services POSIX)
years 2000: denomination OS/390 disappears with the profit from Z/OS. Mode 64 bits; opening to Internet (Websphere), TCP/IP.

External bonds

Historical
Course OS/390

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