Volume table of contents

In the IBM mainframe storage architecture, Volume Table Of Contents, or VTOC, is a data structure that provides a way of locating the data sets that reside on a particular disk volume. It is the functional equivalent of the root directory of a mass storage device (floppy, jump drive, hard disk, etc.) on a PC or minicomputer, e.g. / on Unix or Linux, C:\ on MS-DOS or Microsoft Windows, can reside within the first 64K tracks on the volume, and lists the names of each data set on the volume as well as size, location, and permissions. Additionally, it contains an entry for every area of contiguous free space on the volume. The third record on the first track of the first cylinder of any volume of DASD (i.e. disk pack) is known as the volume label and must contain a pointer to the location of the VTOC. A VTOC is added to a disk when it is initialized using the Device Support Facilities utility program, ICKDSF. VTOC was originally designed for removable disk packs.