The system automatically constructs a DSCB when space is requested for a data set on a direct access volume. Each data set on a direct access volume has one or more DSCBs to describe its characteristics. The DSCB appears in the VTOC and, in addition to space allocation and other control information, contains operating system data, device-dependent information, and data set characteristics. There are seven kinds of DSCBs, each with a different purpose and a different format number. See z/OS DFSMSdfp Advanced Services for an explanation of format-1 through format-9 DSCBs. Format 0 DSCBs are used to show empty space in the VTOC.