You can store data on secondary storage devices, such as a direct access storage device (DASD) or magnetic tape volume. The term DASD applies to disks or to a mass storage medium on which a computer stores data. A volume is a standard unit of secondary storage. You can store all types of data sets on DASD but only sequential data sets on magnetic tape. Mountable tape volumes can reside in an automated tape library. For information about magnetic tape volumes, see z/OS DFSMS Using Magnetic Tapesz/OS DFSMS Using Magnetic Tapes. You can also direct a sequential data set to or from spool, a UNIX file, a TSO/E terminal, a unit record device, virtual I/O (VIO), or a dummy data set.

Each block of data on a DASD volume has a distinct location and a unique address, making it possible to find any record without extensive searching. You can store and retrieve records either directly or sequentially. Use DASD volumes for storing data and executable programs, including the operating system itself, and for temporary working storage. You can use one DASD volume for many different data sets, and reallocate or reuse space on the volume.

Data management is the part of the operating system that organizes, identifies, stores, catalogs, and retrieves all the information (including programs) that your installation uses. Data management does these main tasks:

• Sets aside (allocates) space on DASD volumes.
• Automatically retrieves cataloged data sets by name.
• Mounts magnetic tape volumes in the drive.
• Establishes a logical connection between the application program and the medium.
• Controls access to data.
• Transfers data between the application program and the medium.