Mainframes

Explanation of Identification Division

A Division is a block of code, which contains one or more sections or set of sections or set of sentences or block of statements.

It begins with division name and ends at the beginning of the next division or at the end of the program.

Divisions are known as system defined words.

All Divisions should be coded in AREA A.

Identification Division provides the program name and other items used to uniquely identify the program.
This division is required in every COBOL program.

In other words, the identification is used to identify the programmer who has write program and it may contain optional
entries like Author,Installation, Date-written, Date-compiled and security depending on the requirement.

PROGRAM-ID is a keyword and it must be specified immediately after the identification division and it is mandatory
in COBOL PROGRAM.

Program name can be up to 8 Characters MAXIMUM.

All the entries in Identification Division should be coded in AREA A.

The Complete syntax of the Identification Division is as follows.

Syntax:

[Mandatory] Identification Division.

[Mandatory] Program-id. Name of the Program.

[Optional] Installation. Development-Center.

[Optional] Date-Written. mm/dd/yy.

[Optional] Date-Compiled. mm/dd/yy. HH:MM:SS.

[Optional] Security. Program-type.


Program- id:

The name of the program will be updated with program-id.

The Length of the program name is up to 8 characters maximum.

By using the program name provided with program-id, the load module will be created after the compilation.

To Execute the program, the name provided with program-id needs to be provided in JCL or in PPT enteries.

The actual source name and name provided with program-id may not be same in all cases.

This is a Mandatory entry(Program-id).


Author:

It describes the name of the programmer who written the program.

This is comment entry which is set of character from the computer character set.

The Comment entry can be written any number of lines before starting another statement in AREA A.

This is optional in Identification Division.


Installation:

It describes the name of the location or company where they installed.

This is also a comment entry.

This is optional in Identification Division.


Date-Written:

It describes the actual date of the program written.

This is also a comment entry.

This is optional in Identification Division.


Date-Compiled:

It describes the actual date of the program compiled.

Date-Compiled details are automatically written by the compiler during the compilation time.

This is also a comment entry.

This is optional in Identification Division.


Security:

The Security describes the confidentiality level of the program.

This is also a comment entry.

This is optional in Identification Division.


Practical Example:

A Simple Program with all entries of identification division was coded like below.


Program Code:

Identification Division.

Program-id. FIRST.

Author Ajay.

Installation SEPT 2015.

Date-Written 06/06/2016.

Date-Compiled. 06/06/2016.

Security Private.

Environment Division.

Data Division.

Procedure Division.

Display 'Identification Division with all entries'.
stop run.

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Structure of COBOL Program

The Structure of the Cobol applies for COBOL Source Program which has set of syntactically correct set of statements.

In other words, COBOL Source Program contains set of syntactically correct set of statements.

Cobol Programs contains hierarchical in structure which was shown in the above diagram.

The COBOL Program hierarchy consists of Divisions, Sections, Paragraphs, Sentences and Statements.

In other words, Each division may contain one or more sections, Each section may contain one or more paragraphs,
Each paragraph contains one or more sentences and each section contains one or more statements.

Each element of the hierarchy consists of one or more subordinate elements.

Divisions➤Sections➤Paragraphs➤Sentences➤Statements.

Discuss them in reverse order for better understanding

Statements:

It consists of a COBOL verb and an operand or operands describes about COBOL verb process on the operands either
it may be a conditional or unconditional.

A statement should have COBOL verb with an operand and may or may not marked with period at the end.

All statements should be code in the AREA B and should not in AREA A.

There are four categories of statements in COBOL.

1. Imperative

2. Conditional

3. Delimited Scope

4. Compiler directing

Example: ADD A TO B GIVING C.

Sentences:

As stated above, a sentence contains one or more statements and those are marked with a period at the last line.

If those are marked with a period in middle, then it will be treated as statement and those are not considered
as sentence.

All sentences also should code in AREA B not in AREA A.

Example:

Move P to Temp
Move Q to P
Move temp to Q.



Paragraphs:

It is a block of code which contains one or more sentences or a set of statements.

A Paragraph begins with the paragraph name and ends at the next paragraph starting.

A Paragraph can be ended in another way at another section starts or at the end of the program.

All paragraphs should code in the AREA A.

Syntax: Paragraph-name.


Sections:

It is a block of code which contains one or more paragraphs or a set of sentences or a block of statements.

Section begins with the section name and ends at another section starting or at the end of the program.

All Sections should code in the AREA A.

Syntax: (section-name) SECTION.


Divisions:

It is a block of code which contains one or more sections or a set of sections or set of sentences or a block of statements.

Division begins with the division name and ends at another division starting or at the end of the program.

All divisions should code in the AREA A.

There are four divisions in COBOL

1. Identification Division.

2. Environment Division.

3. Data Division.

4. Procedure Division.

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Cobol Coding Sheet

In olden days, COBOL programs needs to be punched on the card and it will be loaded to punch card reader.

For to identify the program coding by the punch card reader,there was a need of coding sheet.

The Cobol coding sheet was a structure to identify from where the cobol coding statements punched or started writing
to differentiate the statements from other.

The COBOL coding structure is known as COBOL Coding Sheet.

In these days, Punched cards are replaced by Editors but the same coding sheet was used to code the COBOL
Programs.

Coding Area contains 80 Columns for each line or row.


Following are the COBOL Coding Rules:

➤ The First Six Character Positions are reserved for sequence numbers.

➤ The Seventh character position is reserved for the continuation character, or for an Asterisk that denotes
a Comment line.

➤ The Actual Program text Starts in Column 8.

➤ Four Positions from 8 to 11 are known as Area A, and Positions from 12 to 72 are Area B.

➤ All Division names, Section names, Paragraph names, File Description (FD) entries and 01 level numbers must start
in Area A.

➤ All other sentences must start in Area B.


Below Coding Sheet will explain the same in detail


1++++678++1112+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++7273++++++++++++++80(Column Numbers).


On Coding Forms,

1 to 6 Columns

These are treated as Sequence Numbers.

➤ 1 to 3 Columns:

Reserved for Page number. Page numbers will be automatically increased along with the lines of code adding
to the program.

➤ 4 to 6 Columns:

Reserved for Line number. Line numbers will be automatically increased along with the lines of code adding.

➤7th Columns:

Reserved for Special Characteristics.

Those are the following.

*

It is used for commenting a line. If the * is coded on the 7th column in the program, the Cobol Compiler
will consider as Comment instead of code.

-

It is used for continuation of previous line. If - is coded on the 7th column in the program, the cobol
compiler will understand that the current line is continuation of previous line.

/

It is used for Printer Stopper.

D

It is debugging indicator. If the D is coded on the 7th column in the program, the cobol compiler will understand
that the current line is used for debugging purpose which will enabled when DEBUGGING MODE enabled in the program.
In all other cases, it will consider as Dummy Line.


8 To 72 Columns

It is the body of the program where the Cobol program can be coded.

The Cobol body was divided into Two Areas.

➽ 8 to 11 Columns:

All Divisions, Sections, Paragraphs, File Description (FD) entries and 01,77 level numbers must start in Area A.

➽ 12 to 72 Columns:

All other Statements, Sentences should be coding in Area B.


73 to 80 Columns

➢ System Generated Number.

➢ It is used for identification Purpose.

➢ COBOL Compiler will not consider this as a part of the program.

➢ While Printing it will be considered to print, hence system will consider 80 characters per line for print.


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Introduction to Cobol

Cobol is an acronym for Common Business Oriented Language where it is primarily developed for Business, Finance and Administrative
System Needs.

It is a high-level programming language very first developed by CODASYL committee (Conference on data systems languages)
in the early of the 1960s (the first compiler is implemented in the same year).

After that, it was assigned to the American National Standards Institute (ANSI) for developing new COBOL standards.

There are three ANSI standards for COBOL that have been developed in the respective years 1968, 1974 and 1985.

ANSI Cobol 1968 - It developed the standard form of the language in 1968 to overcome the problem of incompatibility between
versions and the version is known as American National Standard (ANS) Cobol.

Cobol 1974 - ANSI published a revised version of (ANS) COBOL which contains an additional set of features.

Cobol 1985 - ANSI published another revised version with new features like scope terminators,
which includes END-IF, END-PERFORM ..etc

Cobol 2002 and Object Oriented Cobol - The language version which is using today contains object orientation.

Some Characteristics of COBOL

Cobol is Self-Documenting

One of the design goals for COBOL was to make it possible for non-programmers such as supervisors, managers, and users to read
and understand the COBOL code.

Cobol is Simple

It is a simple language. No pointers, no user-defined functions, no user-defined types and a limited scope of function.

Cobol applications regularly run-in critical business areas.

A Cobol application deals with a large number of data regularly.

Example: Bank Transactions.

Different Environments using COBOL programs

Based on the usage of COBOL and using the program execution, the application programs can be divided into two types.

1. Batch.

2. Online.

Let's discuss the differences between batch and online COBOL programming.


Batch Programming

Batch Programs needed JCL (JOB CONTROL LANGUAGE) to EXECUTE.

Online Programming

Online Programs did not need any other language to execute and will trigger immediately when the task initiated by the user.


Batch Programming

These programs contain COBOL, can be used with the below combination of programming languages which are optional.

➤ COBOL Programs.

➤ COBOL+DB2 Programs.

➤ COBOL+DB2+VSAM Programs.

➤ COBOL+DB2+VSAM+IMS DB Programs.

Online Programming

These programs contain COBOL+CICS, can be used with the below combination of programming languages which are optional.

➤ COBOL+CICS Programs.

➤ COBOL+DB2+CICS Programs.

➤ COBOL+DB2+VSAM+CICS Programs.

➤ COBOL+DB2+VSAM+CICS+IMS DB Programs.


Batch Programming

Batch is run detached from a terminal.

Online Programming

Online is run connected to a terminal to initiate the tasks.


Batch is program driven.

Online is data driven.


Batch Processing is execution of a series of Programs ("jobs") on a computer without manual intervention.

Online Programs Prompt the user to provide the input.


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Advantages of Mainframe Computers

✦ Availbility

➤ The recent mainframe systems Z series are designed to provide availability of 99.999%.


✦ Scalability

➤ The ability of a system to expand as resources, such as processors, memory, or storage are deleted.


✦ Reliability

➤ It is a measurement of the ability of a system to continue processing without failure.

➤ The "Z" in the system Z's brand name stands for Zero down-time.

➤ System Z servers have reported a 'Mean Time to failure' of 40 years, which means they are guaranteed to run
continuously for 40 years without any failure.


✦ Compatibility

➤ Programs written for the IBM OS/360 and later models will still run quite happily on the latest version
of IBM Z/OS, usually without even a recompile or re-assembly (that's nearly 50 years of continuous upward compatibility
and reliability).

➤ IBM has been maintaining downward compatibility for every new release of hardware and software.


✦ Redundancy

➤ One of the most obvious benefits of the mainframe environment is the incredible amount of redundancy
that the mainframe features.

➤ It is the use of several identical functional units, such as several disk drives or power supply systems,
within one computer system in order to provide data security and a certain degree of fault tolerance in case of
hardware failures.

➤ Redundancy power supplies, processors and storage devices create a system that practically can't be taken offline.


✦ Customization

➤ Mainframes are able to be completely customized to fit an individual user's need.

➤ The mainframes is built to order by ibm and thoroughly tested to ensure that it meets customer requirements.

➤ Individual processors can be turned on and off on real-time needs, and operating parameters are completely customizable.

➤ Additionally, it is possible to run multiple operating systems or Z/OS instances on multiple logical partitions at the same time.

➤ Additionally, most large companies have applications developed or customized to specially meet unique business needs.

➤ Estimates that up to 70 % or percentage of corporate production data still resides on the mainframe.

➤ This means that private clouds residing on system Z have secure access to essential information that can be shared if necessary
with adequate access controls, encryption, data security, data masking and integrity.


✦ Security

➤ Modern mainframes have security built into them from the ground up, both in the operating system and through
cryptographic hardware acceleration.

➤ Governments, Univerisities and large-scale enterprises like banks, insurance companies.. etc.

➤ All of whom have a critical requirement to keep user and internal data protected at once protected but also highly retrievable.

➤ At the kind of high-demand loads we talked about in the first point, you will begin to see the daunting nature of that task
when you realize, for example, that all of those hundreds of thousands of requests that VISA processes every second have to be both
encrypted and decrypted in real-time.

➤ I.E., At a speed that won't be noticeable to those hundreds of thousands of simultaneous users.

➤ It's a task that lower-powered servers aren't quite up to - but one which built-in hardware acceleration of
the encryption and decryption processes help the mainframe excel at.

➤ There is not a single incident of virus or worm or spyware or malware attack in the last 50 years history of a mainframe.

➤ The power of IBM's Z system processor can move mountains of data, billions of instructions and supports
parallel processing.

➤ A batch job that copies billions of records from one file to another file structure can take minutes instead of hours.

➤ Multiprocessing of hundreds of simultaneous users, system tasks, online service and batch jobs will not crash a processor:
a mainframe LPAR image is designed to handle heavy loads.

➤ The processor will not crash from overuse or overheating like ordinary computers.

➤ The latest Z13 mainframe uses the most powerful processor on the planet. The Z13 supports up to 8000 Linux
images simultaneously for cloud computing.

➤ For the mobile economy the Z13 does real-time encryption and can process 2.5 billion transactions per day.



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Characteristics Features of Mainframe Operating System

♨ Virtual Storage:

In most computer systems, the processor's main storage is among the most valuable of the systems resources.

As a result, modern mainframe computer operating systems provide sophisticated services to make the best use of the available main storage.

Among the most important of these services is virtual storage.

Virtual storage is a technique that lets a processor simulate an amount of main storage that is larger than the actual amount of real storage.

For example, a processor that has 2M bytes of real storage might use virtual storage to simulate 16M bytes of main storage.

To do this, the computer uses disk storage as an extension of real storage

The key to understanding virtual storage is realizing that at any given moment, only the current program instruction and
the data it accesses need to be in real storage. Other data and instructions can be placed temporarily on disk storage,
and recalled into main storage when needed.

In other words, virtual storage operating systems transfer data and instructions between real storage and disk storage as they are needed.

Although the details of how an operating system implements virtual storage varies from one system to the next, the basic concept is the same.

Fortunately, virtual storage is largely trans-parent from the users point of view, virtual storage appears to be real storage.


♨ Multiprogramming:

Multiprogramming means that the computer lets more than one program execute at the same time, i.e., at any given moment, only one program can have control of the CPU.

Some processing operations like reading data from an input device - take much longer than others.

As a result, most programs that run on mainframe computers are idle a large percentage of the time, waiting for I/O operations to complete.

If programs were run one at a time on a mainframe computer, the CPU would spend most of its time waiting.

Multiprogramming simply reclaims the CPU during these idle periods and lets another program execute.

♨ Spooling:

It means Simultaneous Peripherals Operations On Line.

A significant problem which must be overcome by multiprogramming systems is sharing access to input and output devices for the programs that execute together.

For example, if two programs executing at the same time try to write output to a printer, the output from both programs is intermixed in the printout.

One way to avoid this problem is to give one of the programs complete control of the printer, which defeats the purpose of multi programming because the other program has to wait until the printer is available.

To provide shared access to printer devices, spooling is used.

Spooling manages printer output for applications by intercepting printer output and directing it to a disk device instead.

When the program finishes, the operating system collects its spooled print output and directs it to the printer.

In a multiprogramming environment, the operating system stores the spooled output separately on the disk so that it can print each programs output separately.

♨ Batch Processing:

A batch file contains a series of commands that are processed together as a batch.

In batch processing multiple programs are processed (works is processed) in units called jobs. Jobs are submitted in batch and
will be executed in sequence.

The data will be provided along with job so no user interaction will take place.

One of the problems that arise when batch processing is used is managing how work flows through the system.

To manage this in the multi-user system, the Job Entry Subsystem (JES) processes each users job in an orderly fashion.

♨ Time Sharing:

It is the another feature of MVS in each each job will be alloted with certain piece of job and each user feels as CPU time is alloted
for it only.

In a time-sharing system, each user has access to the system through a terminal device.

Instead of submitting jobs that are scheduled for later execution, the user enters commands that are processed immediately.

Hence this is sometimes called "Interactive Processing", as it allows users to interact directly with the computer.

Time-share processing is called "Foreground Processing" and batch job processing is called "Background Processing".


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Evolution Of Z / OS (zero downtime operating system)

Primary Control Program(PCP):

➽ It was the first release of OS version by IBM in the year 1965. It had limited capabilities and it doesn't offer multi
programming, no priority scheduling and no spooling facility.

It was an unreliable system and became obsolete in the year 1969.

➽ Multiprogramming concept was introduced with the introduction of MFT and MVT.

MFT: Multi programming with fixed number of tasks.

MVT: Multiprogramming with variable number of tasks. It was the first reliable system and both MVT and MFT provide limited spooling
capability.

HASP(Houston Automatic Spooling Priority):

A group of IBM employees developed a package that is superimposed on MFT or MVT and provides good spooling capabilities.

ASP(Attached Support Processor):

It is another package developed for MVT that would allow several mainframes to work together under one operating system
in a master or slave relationship.

OS/VS OR System/370:

In this virtual storage capabilities were provided and new hardware VS1 and VS2.

VS1 was basically an MFT system in a virtual environment. VS2 has two versions SVS(Single Virtual Storage) and MVS (Multiple Virtual Storage)

➽ In 1987 only MVS was left behind and MVS along with HAS was named as JES2(Job entry subsystem) and MVS along with ASP was named as JES3(Job entry subsystem).

➽ MVS provides reliability, integrity and performance. The only drawback was the limited virtual storage capability of 16 MB.

MVS / XA:(Multiple Virtual Storage or Extended Architecture)

It was a new version of MVS having storage availability of 2GB.

MVS / ESA:(Enterprise Systems Archittecture)

It was announced in 1988. In this virtual storage was extended upto 16TB.

Z / OS (zero downtime operating system)

It is the latest version.


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