MULTIPLE VIRTUAL STORAGE

Now it’s time to know about MVS. As I told earlier that this is very important topic and vast topic.so i am dividing this into 2 parts so as to make you easy to read.In first part i will explain about virtual storage in second part Multiprogramming and MVS functions.MVS is an operating system to mainframe computers. "MVS operating system". Now I will elaborate and tell you that MVS is nothing but "MULTIPLE VIRTUAL STORAGE".Before going deep into the concept let me tell once again recollect you about languages of mainframes:

• COBOL

• JCL

• VSAM - VIRTUAL STORAGE ACCESS METHOD.

• DB2

• CICS

So now coming to the point MVS is nothing but MULTIPLE VIRTUAL STORAGE SYSTEM. It is related to virtual storage and multiprogramming.Let me explain about these two key points virtual storage and multiprogramming. First one Virtual Storage.

What is virtual storage? Like generally just think with dictionary meaning VIRTUAL.... that means imaginary... which does not exist. So let’s see how it works here. Virtual Storage is technique that allows processor to simulate amount of main storage that is larger than actual amount of real storage. Which stores large amount of data .This is the main advantage of virtual storage. It stores data virtually in temporarily on disks, and recalled into main storage when needed.In other words virtual storage O/S transfers data and instructions between real storage and disk storage as they needee. Only current program instruction and the data are accessed in real storage. For example a processor has 2M bytes of real storage might use virtual storage of 16M bytes of main storage Just think!!!! how the system will do this?? For this computer uses disk storage as an extension of real storage .Implementation of virtual storage varies from one system to another system. The importance of virtual storage can be known well in one of the module called VSAM as i mentioned above.

Here i will explain one more point about how data is stored. Ok shall I ask one question? Ok what is the maximum size of computer’s address space limited to?

Before you get the answer here is some small information about address spaces

Main storage consists of millions of storage individual locations each location stores one character or byte .To refer to particular location we use an address that indicates storage location taking offset from beginning of the memory. It stores Like this:

First byte of storage address to 0

Second byte storage address to 1 so on……

• Now The answer is…………

• MAX. SIZE OF COMPUTER’S ADDRESS IS LIMITED BY THE NUMBER OF DIGIT’S THAT CAN BE USED TO REPRESENT AN ADDRESS.

SYSTEM/370 CANNOT CONTAIN MORE THAN 16M BYTES OF STORAGE

So in this part we learnt about Virtual Storage in MVS PART-2 we will learn about multi programming and function of MVS.