Introduction to CICS

CICS Stands for Customer Information Control System
Why CICS
➤ The main drawback of the batch sytem is multiple processes should not able to run at the same time and the process will not complete instantly.
➤ So, CICS is introduced by IBM in the 1960's to overcome above issue and to support online programming on Mainframes.
➤ It acts like a sub-operating system, it manages its own memory space, controls the concurrent execution of multiple applications.
➤ CICS is it self is a batch program running on mainframes to enable application programs and respond to online requests.
➤ As Shown in the above picture, CICS is a high priority batch job running on mainframe operating system along with other batch jobs.
➤ It acts as a interface between OS and Online Application programs. Online programs are get trigerred by the user by entering a piece
of data on terminals.
➤ Online programs need to be designed in such way that these programs respond to user instantly with required data.
➤ Online reservation system shown in the above picture allows users to enter train number, date.
➤ When user enters the data and press required key then that will be passed to CICS on Mainframes. Then CICS will trigger
corresponding online program and send back the data to user. This process is called transaction.
➤ In CICS every transaction type is defined by 1 to 4 character word called Transaction ID.
➤ One program is attached to this transaction ID and we define this mapping in CICS table called PCT (Program Control Table).
Batch Vs Online Programming
➤ Batch Cobol Programs are executed by OS, By submitting the JCL to operating system, this process is called batch processing.
➤ Cobol Programs (which contains CICS Commands) get executed by CICS, this process is called online processing.
Sample CICS Command

CICS Program Format

➤ In above sample CICS program, you can see there are few CICS commands coded in Cobol program.
➤ Receive command is used to receive data from terminal, Read command is used to read the data from VSAM file.
➤ Return command is used to return the control back to calling program or to CICS itself.
➤ If you observe in this sample program, CICS commands are used to talk with external world like terminals,files,databases, storage control.
➤ Actual logic of the program is written using normal cobol verbs.
➤ We don't use some COBOL Verbs in CICS programs
➤ For Example: OPEN,READ,WRITE,REWRITE,CLOSE. Instead we use CICS commands like CICS READ, WRITE etc..,

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