Free space for certain devices

Only one field in the format-7 DSCB is an intended interface. This field indicates whether the DSCB is a format-7 DSCB. You can reference that field as DS1FMTID or DS5FMTID. A character 7 indicates that the DSCB is a format-7 DSCB, and your program should not modify it.

If you are diagnosing a problem, see z/OS DFSMSdfp Diagnosis for the layout of the Format-7 DSCB.