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DD UNIT Parameter
It is used to specify the input or output device that is to be accessed. In mainframe, all devices have address assigned to them when they are added to the system. Thus these devices can be accessed using this addresses. With use of UNIT parameter we can specify this address. Sometimes certain types of device can be grouped together, and the group give a name. Device can be referenced via group name
Syntax:-
UNIT= device-type | device-address | group-name | (device,,DEFER)
Example:-
//JOB1 JOB A123,’STEVE’
//STEP1 EXEC PGM=PROGRAM1
//DATA1 DD DSN=DEPT1.EMP1.DATA1,
// DISP=(NEW,CATLG,DELETE),
// UNIT=SYSDA
//DATA2 DD DSN=DEPT1.EMP1.DATA2,
// DISP=(NEW,CATLG,DELETE),
// UNIT=3380
In above example, PROGRAM1 will be executed, and file ‘DATA1’ which resides on any of the devices which are grouped under the symbolic name SYSDA will be accessed and file ‘DATA2’ which resides on a 3380 disk unit, will be accessed