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Choosing the Device Type Using BIM-EPIC's JCL Features

7-56 User Reference

Choosing the Device Type

Generic Device Independence (GDI) and Generic Device Independence for Unit Record

Devices (GDIUR), sometimes called storage media independence, allows you to choose the

type of media on which your dataset will be stored. You can process the dataset on either tape

and disk, no matter how the dataset is defined in your program.

In addition, Generic Device Independence for Unit Record devices (GDIUR), allows you to

use disk or tape for datasets that have been defined in your programs as unit record devices

(DTF types DTFCD, DTFPR, DTFCP, and DTFDI). GDIUR can be used for logical units

SYS000 through SYS255, and for SYSIPT, SYSLST, and SYSPCH.

GDIUR greatly simplifies the use of disk for VSE datasets that use the logical units SYSIPT,

SYSLST, and SYSPCH. The following standard VSE JCL could be used to create a disk

dataset on logical unit SYSPCH, and then read that dataset with logical unit SYSIPT:

// DLBL IJSYSPH,'COBOL.PROGRAM',0

// EXTENT SYSPCH,VOL251,1,0,200,2000

ASSGN SYSPCH,DISK,VOL=VOL251,SHR

// EXEC DFHECP1$

CLOSE SYSPCH,PUNCH

// DLBL IJSYSIN,'COBOL.PROGRAM'

// EXTENT SYSIPT,VOL251

ASSGN SYSIPT,DISK,VOL=VOL251,SHR

// EXEC FCOBOL

CLOSE SYSIPT,SYSRDR

There are two problems with this approach:

• If the first step (DFHECP1$) cancels, SYSPCH will remain permanently assigned to

disk. Manual intervention or additional JCL is needed to re-assign SYSPCH correctly.

•

If the second step (FCOBOL) cancels, SYSIPT remains permanently assigned to disk.

Manual intervention or additional JCL is needed to re-assign SYSIPT correctly.

In addition, the JCL required is complex and lengthy, especially when compared to the

following BIM-EPIC JCL which accomplishes the same task:

* //IJSYSPH DD DSN=$$$.COBOL,UNIT=DISK,DISP=(,KEEP,DELETE)

// EXEC DFHECP1$

* //IJSYSIN DD DSN=$$$.COBOL,DISP=(OLD,DELETE)

Note that no ASSGN or CLOSE statements are needed, because GDIUR ensures that system

logical units can never be left erroneously assigned to disk.

Programs that use GDIUR can also take advantage of BIM-EPIC's reblocking facility to save

disk space and improve performance.

Generic Device

Independence

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Memorex LOCK - VERSION 2-24 Spezifikationen Seite 276