MULTIPLE VIRTUAL STORAGE

Now in this MVS part-2 we will learn about multiprogramming and MVS functions. Let's see about Multiprogramming. In earlier days processing of jobs could not handle the work demand to deliver work more quickly and efficiently. When system is requested for a specific function such as printing or updating of files they were submitted for processing one at a time. The operating system would process a job in a completely sequential manner i.e one by one process. Which when compared to electronic speed of processor were very slow. While jobs were temporarily bottle-necked in computer to perform i/o operation to complete, processor remains idle. This method is very inefficient since processor time is wasted. To solve this problem multiprogramming is developed. See, here I will explain clearly how this multiprogramming happens. When a request is araised to execute a job in which already another job is executing, the operating system temporarily stops the job by interrupting it. This allows CPU to take another job and process it. Before interrupting the job while CPU is taking another, the processor will save all relevant data about the job, so that it can easily be restored.

• Objective of multiprogramming is to keep all major computer resources busy because different job has different requirements like some job needs lot of i/o resources. It is necessary for a system for optimum utilization.
  

• In multiprogramming environment a number of programs share the memory along with operating ystem.It performs complex operations such as protection of each job make instantaneous decisions of allocating job resources.
  

If we go on telling about virtual storage and multiprogramming there are lot’s to tell but as if now this information is sufficient. I think now you understood about Virtual storage and multiprogramming

SO if we combine these two virtual and multiprogramming which is close related to MVS topic the functions of MVS are below:

• MVS operating system is a group of related program that govern computer

• This operating system controls the execution of the program and provides services necessary to make use of computer system.

• MVS manages the storage capacity to make it appear a lot bigger than it is in reality so that it can allow many users to utilize maximum amount of data.

• It translates jobs to execute fastly and fast response time when processing interactively.

• MVS supports more than one address space at a time.

• MVS keeps only active portions of each program in the real storage and stores the rest of code and data in special data sets usually in DASD.

DASD – DIRECT ACCESS STORAGE DEVICE.

• Methodology to communicate what particular resources given job needs to MVS is done through JCL.

JCL:-JOB CONTROL LANGUAGE.We had a seperate module for this. This JCL acts as a interface between MVS operating system and JES (JOB ENTRY SUBSYSTEM) its function is to submit job.In detail see JCL module.

• There are two different data management environment that exists under MVS
1. VSAM
2. NON-VSAM

• MVS provides facilities like data to reside on tape, DASD and I/O devices.

These are basics things to learn about MVS in vast we can learn more in JCL and VSAM while explaining these topics again MVS concepts will cover. so up to now this information is enough to learn about MVS.