Indexed and nonindexed VTOCs have similar structures with the following differences for an indexed VTOC:

• Only a single, empty format-5 DSCB exists.
• Some format-4 DSCB data (the number of format-0 DSCBs and the CCHHR of the highest format-1 DSCB) is not maintained by DADSM. The VSE bit (bit 0 in field DS4VTOCI), set to 1 in the format-4 DSCB, indicates that the contents of these fields (and the format-5 DSCB) are not valid. The index bit (bit 7 in field DS4VTOCI) is set in the format-4 DSCB; it indicates that a VTOC index exists.