The VIXM contains a bit map in which each bit represents one VTOC index record. The status of the bit indicates whether the VIR is allocated (1), or unallocated (0). On an extended address volume, the VIXM record header is enlarged to accommodate the volume size, free space statistics for the VTOC and index, free space statistics for the entire volume and from track-managed space. Fields in this expanded header define the RBA of the first VPSM record that maps multicylinder units, along with the minimum allocation unit in cylinders for the VPSMs that map cylinder-managed space.

An area of the VIXM is reserved for VTOC recording facility (VRF) data. (This facility allows detection of and recovery from some errors in an indexed VTOC.)