Direct access storage device

A direct access storage device, or DASD (pronounced DAZ-dee) is a form of magnetic disk storage, historically used in the mainframe and minicomputer (mid-range) environments. A redundant array of independent disks (RAID) is a form of DASD.

"Direct access" means that all data can be accessed directly — in a form of indexing also known as "random access" — as opposed to storage systems based on seeking sequentially through the data (e.g., tape drives).