Cataloged data sets

The operating system has facilities that automatically record the following information about each of your data sets:

The data set name
The serial numbers of the volume or volumes containing the data set
The type of device on which the volumes should be mounted
The data set's relative position on its first volume

The information is indexed by the data set name and recorded on a direct access device in a logical structure called the catalog. You can retrieve a cataloged data set by specifying its name in the DD statement and omitting the volume serial. The system finds the associated information in the catalog and issues a command, to either the operator or the tape library, to mount the cartridge on a drive.