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Some Excerpts from Mainframes360

Q. What are the two broad types of Applications/Systems?
All application/systems are of 2 types
(i) Online Systems(Transaction Processing Systems)
(ii)Batch Processing Systems. Read more ...

Q. What is the DATA DIVSION? What are the different sections in the DATA DIVISION?
DATA DIVISION is used to describe the Input Output Storage areas and temporary storage areas. In other words, it’ll describe the structure of the data being stored in Input Output Files, as well as in any temporary storage. Read more ...

Q. What are data-types? What are the basic data-types in COBOL?
Data-type is used to announce/declare to the MVS O/S, about the type of data you’re gonna store in a Storage Location, so that it can estimate the storage space to be allocated and reserved for you data excusively. Read more ...

Q. What are group and Elementary Data Items?
In COBOL, one or more elementary data-items can be grouped together. For example, we can group EMP-NAME, EMP-SALARY and EMP-JDATE as EMPLOYEE-RECORD. In COBOL, we say that a group item is a data item, which has several low-level(elementary) data-items. Read more ...

Q. Can you elaborate on how to write the File Descriptor FD Paragraph?
As mentioned before, we must describe the input file record format and output file record format in the File Descriptor FD paragraph under the FILE SECTION. Remember, that FD paragraph is always coded in AREA A. Read more ...

Q. What is JOB Log? Why do we need a JOB Log? What purpose does it serve?
When you submit a Batch JOB/JCL to the MVS System, the MVS executes the Job Stream, makes the necessary resources available to the the EXEC PGM (Program), and finally tells you the result of the Job. Read more ...

Q. In the previous tutorial, you’ve stated what is compiling, linking and running.. Can you show me a Compiler and Linking JCL/Job Stream that does this?
Sure, as you know, the Compiler takes a SYSIN DD Input Dataset, which is the Source COBOL Program. The COBOL Compiler IGYWC(or IGYCRCTL) produces SYSOUT DD Dataset containing the JOB Log and Status messages, and more importantly, SYSLIN DD which is Object Module and Input for the Linker. Read more ...

Q. Show me a simple JCL/JOB Stream to run my COBOL Program(LOAD MODULE).
On Windows, to run a program, we simply click on the Executable File. In the same way, to run our COBOL Program on Mainframes, we are going to use the LOAD MODULE(Executable). To run a program on the MVS, you write JCL. You specify the name of the Program(LOAD MODULE) Read more ...

Q. What is the ENVIRONMENT DIVISION? What purpose does it serve in the COBOL Program?
The ENVIRONMENT DIVISION provides information about the computer equipment/configuration upon which the COBOL program will run. It also gives the name of the input and output files used in the program. It assigns the file-names to ddnames(DD Statements in the Run JCL). Read more ...

Q. What is a Mainframe Computer?
A Mainframe computer is used by large organisations for processing huge volumes of data e.g. census, consumer statistics, ERP and financial transaction processing. Read more ...

Q. How did IBM Mainframe machines evolve?
Well, IBM first launched the System/360, then System/370, System 370/XA, Enterprise System Architecture(ESA)/370, System 390 and the latest machines in the Mainframe series is zSeries(pronounce Zee). Read more ...

Q. What does a Mainframe Computer look like? How do you operate it?
Let’s just try to see what’s life like, if you are Mainframe machine’s operator. A Desktop computer can fit into a trolley or a cabinet. A Mainframe Machine is generally big monster-size, would fill up a room. On a Desktop PC, you would sit near the physical computer and operate it using the keyboard and the mouse, and see the result on the monitor. Read more ...

Q. Hey, Windows is the most popular Operating System on a Desktop-PC. On the same lines, the popular Mainframes Operating System is MVS...
Bulls-eye! In fact, MVS is said to be the Operating System that makes the world move. Read more ...

Q. What about Super-computers? Are mainframes faster than super-computers?
Don’t equate the word Mainframes to Speed. Mainframes have tremendous processing power or computational power, but of a different kind. Think of task, where we have 1,00,000 records of Input data, and we want to perform 3 calculations on each record, and then put the Output Records in a separate file. Read more ...

Q. What’s that name again.. Multiple Virtual Storage? What crap?
Virtual Storage is a simple idea. Virtual storage simulates a large amount of main storage(Primary or main memory) by treating the auxiliary storage as an extension of the real storage. Thus, a program gets the feel, “Wow, I have an infinite amount of computer memory at my disposal.” Read more ...

Q. What is a Batch Job?
If you are a college student, you would have probably written a computer application in C, and executed it on your desktop PC. You run the program interactively, you type in some input data, wait for the response(output), and then you type some more input, and this cycle continues. Such programs or systems are called as Online Systems or Transaction Processing Systems. Read more ...

Q. Look, on Windows PC, you interact with the computer using the Windows GUI – the Desktop Icons, the Menus, Buttons etc. How do you interact with an MVS Mainframe System?
MVS offers several ways to interact with it. The 3 main ways of interacting with MVS are TSO, ISPF and CICS. Read more ...

Q. What does COBOL stand for? What are the application areas where COBOL Programs written?
COBOL stands for Common Business Oriented Language. COBOL Programs are used for commercial data processing. COBOL is an English-like language. Writing a COBOL program is just like writing a passage in English. Read more ...

Q. You said COBOL Programming language bears resemblance with English. Do COBOL Programs have paragraphs like in English?
A COBOL Program consists of 4 main divisions : IDENTIFICATION DIVISION, ENVIRONMENT DIVISION, DATA DIVISION and PROCEDURE DIVISION. IDENTIFICATION DIVISION is used to identify the COBOL Program to the system. It tells the... Read more ...

Q. Show me the basic skeleton of a COBOL Program then..
The basic skeleton of a COBOL Program is as follows : IDENTIFICATION DIVISION. ENVIRONMENT DIVISION. Read more ...

Q. Paragraphs in the English language are indented. Do you have indentation/alignment rules in COBOL?
Just like paragraphs in English, COBOL Divisions and Paragraphs must follow strict alignment rules. The way we indent paragraphs in English, you must indent different Divisions, sections and paragraphs in a COBOL Program. When you write .. Read more ...

Q. What is the IDENTIFICATION DIVISION used for?
The IDENTIFICATION DIVISION is used to identify the COBOL Program to the system. It has the following paragraphs :
PROGRAM-ID.
AUTHOR.

Read more ...

Q. What does the PROCEDURE DIVISION look like? What’s the format/syntax. Can you elaborate..
The PROCEDURE DIVISION indicates the entry-point or starting point of the COBOL Program. This is where the computer system begins to run(execute the COBOL instructions). Hence, all your instructions/programming logic must be written inside this PROCEDURE DIVISION. Read more ...

Q. How do you compile a COBOL Program? What is meant by Linking a COBOL Program? Finally, how do you run the Program on a Mainframe System?
Compiling a COBOL Program : COBOL is a high-level language. The Mainframe Computer System only understands binary Machine Language 0 and 1. Thus, your COBOL Program has to be translated from COBOL Language to Binary Machine Language. So, you give the Program in COBOL Language as Input to the Translator(Compiler), and you get the Output Program in Binary Machine Language. Read more ...

Q. Could you throw some light on the WORKING-STORAGE SECTION of a COBOL Program?
The WORKING-STORAGE SECTION is used to declare any fields or records that are not going to be used in input files, or output files, but they are used to store the intermediate results of processing in a temporary storage area. Read more ...

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Saturday, August 1, 2009