JCL - EXEC Statement

Each JCL can be made of many job steps. Each job step can execute a program directly or can call a procedure, which in turn executes one or more programs (job steps). The statement, which holds the job step program/procedure information is the EXEC statement.
The purpose of the EXEC statement is to provide required information for the program/procedure executed in the job step. Parameters coded in this statement can pass data to the program in execution, can override certain parameters of JOB statement and can pass parameters to the procedure if the EXEC statement calls a procedure instead of directly executing a program.
Following is the basic syntax of a JCL EXEC statement:
//Step-name EXEC Positional-param, Keyword-param 
Let us see the description of the terms used in above EXEC statement syntax.
This identifies the job step within the JCL. It can be of length 1 to 8 with alphanumeric characters.
This is the keyword to identify it as an EXEC statement.
These are positional parameters, which can be of two types:
Following are the various keyword parameters for EXEC statement. You can use one or more parameters based on requirements and they are separated by comma:
Used to provide parametrized data to the program that is being executed in the job step. This is a program dependant field and do not have definite rules, except that the PARM value has to be included within quotation in the event of having special characters.
For example given below, the value "CUST1000" is passed as an alphanumeric value to the program. If the program is in COBOL, the value passed through a PARM parameter in a JCL is received in the LINKAGE SECTION of the program.
This is used to specify whether the job step require virtual or real storage for execution. Virtual storage is pageable whereas real storage is not and is placed in the main memory for execution. Job steps, which require faster execution can be placed in real storage. Following is the syntax:
ADDRSPC=VIRT | REAL
When an ADDRSPC is not coded, VIRT is the default one.
This specifies the accounting information of the job step. Following is the syntax:
ACCT=(userid)
This is similar to the positional parameter accounting information in the JOB statement. If it is coded both in JOB and EXEC statement, then the accounting information in JOB statement applies to all job steps where an ACCT parameter is not coded. The ACCT parameter in an EXEC statement will override the one present in the JOB statement for that job step only.
If REGION is coded in an EXEC statement, then it applies to that job step only.
REGION coded in JOB statement overrides the REGION coded in EXEC statement of any job step.
Used to control the job step execution based on the return-code of the previous step.
If a COND parameter is coded in an EXEC statement of a job step, then the COND parameter of the JOB statement (if present) is ignored. The various tests that can be performed using a COND parameter is explained in conditional Processing.
Following is a simple example of JCL script along with JOB and EXEC statements:
//TTYYSAMP JOB 'TUTO',CLASS=6,MSGCLASS=X,REGION=8K,
//      NOTIFY=&SYSUID
//*
//STEP010 EXEC PGM=MYCOBOL,PARAM=CUST1000,