TIME SHARING OPTION

TSO stands for TIME SHARING OPTION as the word itself refers sharing it allows users to share time and resources. It is an optional feature of MVS that provides time sharing capabilities. So how to access TSO? After loading software connect t o the terminal enter LOGON command this command looks like

• LOGON USER-ID/PASSWORD

Its better that your user-id look like USER-ID.NAME.TYPE

• USER-ID is the TSO user identification number assigned to each use.

• NAME is the name that you create to identify the dataset.

• TYPE is one of the values used to identify the type of data stored in the data set.

If you want to logoff from the session then type the command LOGOFF.

In TSO you need to create and modify datasets. Here datasets are two types

• PS - Physical Sequential

• PDS – Partitioned Data Set

I will tell what are these two

• Physical Sequential Data Set -It is plain and contain does not contain any directories
  

• Partitioned Data Set - It is also like Indexed because it contains directories and data set as members

For better understanding purpose:

Just think or imagine PS to DOS Modifier because in that we can create only one file. PDS to DOS directory because in directory we can create n number of files in datasets module I will explain more about PS and PDS.If you can able to understand the difference between these two it is easy to create datasets.

SOME FUNCTIONS AVAILABLE UNDER TSO

• DATASET MANAGEMENT FUNCTIONS

• DYNAMICALLY ALLOCATE DATASET

• LIST, PRINT, COPY DATA SETS

• DELETE, RENAME DATASETS

• LIST CATALOG ENTRIES

• LIST VTOC ENTRIES

• VTOC - VOLUME TABLE OF CONTENT

• LIST VSAM AMS COMMANDS

• AMS – ACCESS METHOD SERVICES

PROGRAM DEVELOPMENT FUNCTIONS

• CREATE AND EDIT PROGRAM LIBRARIES

• COMPILE A SOURCE PROGRAM

• LINK-EDIT A COMPILE PROGRAM

• TEST A LINK-EDITED PROGRAM

BATCH JOB FUNCTIONS

• SUBMIT A JOB

• MONITOR THE PROGRESS AND VIEW OUTPUT OF BACKGROUND JOB

• IF NECESSASRY CANCEL SUBMITTED JOBS

OTHER TSO FUNCTIONS

• HELP FACILITY

• CLIST

• REXX

Here is your TSO session looks like Here i am giving you an brief idea how it looks like to make
you understand very easily

1. LOGON TSO USER ID & PASSWORD

USERID

PASSWORD

PRESS ENTER

Now 2nd screen

2.ISPF PRIMARY OPEN MODE

(Enter command or any of the down options like 3 or 2…) · 0. SETTINGS - TERMINAL AND USER PARAMETES · 1. VIEW - DISPLAY SOURCE DATA & LISTING · 2. EDIT - CREATE OR CHANGE SOURCE DATA · 3. UTILITIES - PERFORM UTILITY FUNCTIONS · 4. FOREGROUND - INTERACTIVE LANGUAGE PROCESSING · 5. BATCH - SUBMIT JOB FOR LANGUAGE PROCESSINNG · 6. COMMAND - ENTER TSO COMMAND OR CL LIST · 7. DIALOGTEST - PERFORM DIALOUGE TESTING · 8. LM UTILITIES- PERFORM LIBRARY ADMINISTRATOR UTILITY FUNCTIONS · 9. IBM PRODUCTS – ADDITIONAL IBM PROGRAM DEVELOPMENT PROCESS · 10. SCLM - SOFTWARE CONFIGURATION AND LIBRARY MANAGER · 11. WORKPLACE - ISPF · 12. MORE ---------------------------------------------------------------------------------------- F1-HELP F2 – SPLIT F3 - SAVE & EXIT F4 – RETURN F5- FIND F6 – CHANGE F7 – PAGEUP F8 – PAGE DOWN F9 -SWAP F10 – LEFT F11 - RIGHT F12 - CANCEL

INTERACTIVE SERVICE PRODUCTIVITY FACILITY

When you logon into mainframes you will see one menu called ISPF menu. In TSO i explained how to logon. Once TSO displays its READY message you can invoke ISPF two ways by entering ISPF command and not entering that command .In many installations, a TSO LOGON procedure is created to automatically invoke ISPF when you LOGON.In this case, the READY command will not appear and you do not have to enter ISPF command seperately . This menu has different options and this is the main screen from which you can be able to go to different options. This ISPF is the main working place from where you can do programs with JCL,COBOL,VSAM,CICS so here I am giving the options of ISPF and one more thing as for practicing in home software you can change few options but some of them are quiet standard. So what i am mentioning here are important .So go on reading..

• 0. SETTINGS - TERMINAL AND USER PARAMETES

• 1. VIEW - DISPLAY SOURCE DATA & LISTING

• 2. EDIT - CREATE OR CHANGE SOURCE DATA

• 3. UTILITIES - PERFORM UTILITY FUNCTIONS

• 4. FOREGROUND - INTERACTIVE LANGUAGE

PROCESSING

• 5. BATCH - SUBMIT JOB FOR LANGUAGE

PROCESSINNG

• 6. COMMAND - ENTER TSO COMMAND OR CL LIST

• 7. DIALOGTEST - PERFORM DIALOUGE TESTING

• 8. LM UTILITIES- PERFORM LIBRARY ADMINISTRATOR

UTILITY FUNCTIONS

• 9. IBM PRODUCTS – ADDITIONAL IBM PROGRAM

DEVELOPMENT PROCESS

• 10. SCLM - SOFTWARE CONFIGURATION AND

LIBRARY MANAGER

• 11. WORKPLACE - ISPF

• 12. MORE

After 10^th option few options may vary.. like in companies generally from 11^th option they use tools option like ENDEVOR, Expeditor e.t.c here we can add few changes after that option. Like

• T TUTORIAL – DISPLAY INFORMATION ABOUT ISPF /PDF

• E EXIT - TERMINATE ISPF USING LOG AND LIST DEFAULTS

• C CHANGES – DISPLAY SUMMARY CHANGES FOR RELEASE

• S SDSF - SPOOL DISPLAY SEARCH FACILITY

I will explain in further topics about these options which we use mostly and here one option is there called "SDSF" this is an option where you can see your jobs in spool area. Spool area is nothing but where your list of submitted jobs are seen.Don't worry you can see all this topics in JCL and further modules.

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.

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.

LANGUAGES

Here let me explain very briefly that mainframes contains four different modules they are as listed below:

• COBOL :- (COMMON BUSSINESS ORIENTED LANGUGE)
• JCL :- (JOB CONTROL LANGUAGE)
• VSAM :- (VIRTUAL STORAGE ACESS METHODS)
• DB2 :- (DATA BASEMANAGEMENT SYSTEM)
• CICS :- (CUSTOMER INFORMATION AND CONTROL SYSTEM)

Combination of all these modules is Mainframes.Don't think that there are so many modules to learn ofcourse you need to learn but they are quiet interesting.This mainframes are different to learn compare to other languages. Just you need to know basics to write a program.I will explain each and every module clearly with example programs.To practice mainframes in home you need to get the mainframes software which are easily available.Just bring that and install in your P.C. So as i said working with programs are quiet different compared to other languages but logics are same.So in further chapters i will explain these modules.

CHAPTER 1.1

The central components of mainframe computer systems are processors. MVS runs on processors that are members of system/360-370 family.MVS is nothing but "MULTIPLE VIRTUAL STORAGE" this we will discuss in another chapter because it is a vast subject. Processors of mainframes are frequently asked interview questions so i am discussing it earlier. So please be careful while telling the answer in interviews here is it i will explain.

• SYSTEM/360-370 FAMILY INCLUDES

• SYSTEM/360 MODELS IN 1960'S

• SYSTEM /370 MODELS OF EARLY 1970'S & 3030 MODELS OF LATE 1970'S

• THE 4300 AND 3080 MODELS OF EARLY 1980'S & 3090 MODELS OF LATE 1980'S

• RECENT MEMBERS OF THIS FAMILY ARE ES/9000,S/390 AND Z-SERIES SYSTEMS.

Some installations still run under 4300,3080 and 3090 systems.These processors which we discussed above are popular processors.

I think now you are able to explain the answer.

CHAPTER-1

We will start with an introduction that why to use maifram computers? and advantages compared to other computers.

Mainframe computers can process several million-program instructions per second.Large organizations rely on these room-size systems to handle large programs with lots of data.These Mainframes are mainly used by insurance companies, banks, airline and railway reservation systems. Mainframes have even more access space and also to input/output devies.They have powerful processors.I explained about these processors in chapter 1.1. This power is useful and required by large corporations who have large amount of data process. Here i will give an small and regular example like generally banks has large data they need to update accounts regularly so they need powerful machines to process this data.These large banks use mainframe computers to maintain their customer account records. so that if customer want to withdraw or deposit money at any branch at any time he can acess easily because his data is already getting up-to-date.So from anywhere he can access his account.

we can compare use of mainframes to micro and mini computers also.

Micro Computers are small, single user systems that provide a simple processor and just few input/output devices.The micro computer is also known as "Personel Computer" As we see them regularly in homes and offfices. This is so called "micro" because the fundemental component that allowed the categories development was CPU created on single chip created with introduction of "microprocessors". When larger systems were focussed on productivity of whole department or organization,the micro computer was only effective for single individual's work.

Mini computers are mid range computers were first developed as special-purpose mainframe computers.They were used, for instance,to control machines in a manufacturing unit.However, now they are widely used as general-purpose computers.They are known as Distributed Data processing i.e company processing power is decentralized.That means end users can process at their own micro computers. Mini computers are used by medium sized business and small sites of large organizations.They are used in factories to control automated assembly lines,manufacturing,process control e.t.c

The important thing to note for minicomputers and mainframes is the reliability of the machine. As it generally has to operate 24 hours.Ofcourse in companies every minute of operation is important.If it does not work for a minute also it is calculated as a huge loss for the company so for these purposes micro computers are not prefferd.They have to rely on room-size systems.

Mainframe computers can handle several million-program instructions per second.They have powerful hardware and CPU chips that can support heavy work inflow which can also be used for making complex calculations, and designs.So they are also called as super computers.

ABOUT ME & MY BLOG

HI Friends!! Welcome to my blog.I am sahithi.I am a B.TECH Graduate.After completing Graduation I learnt mainframes. I had gone through many books and websites while learning.I had teaching experience in mainframes. This material in blog is maximum based on Alexis Leon book and institute materials and own programs. I prefer Alexis Leon book to learn many things and it is my most suggestted book.In this blog i will highlight important things to learn from that book..Now u can sit at home relax and just go through my blog .I will try to share my knowledge as much as possible.First i would like to share my knowledge in mainframes.This blog is very good for mainframes starters.I will help you how to study mainframes very easily.Now no need to struggle hard as i had come that long way.I will try my level best to help you to learn material including interview questions .In mainframes i will try to explain each and every key point to understand so as to make you to learn easily.I will explain each and every module.So friends!! are you ready to learn? ok then go through myblog.