Glossary of Hard Disk Drive Terminology (Letter D)

A collection of data stored on a computer system medium, such as a hard drive, CD-ROM, etc., that can be used for more than one purpose.

Data Lifeguard
A Western Digital exclusive data reliability feature that automatically detects, isolates and repairs problem areas on the hard drive before data loss can occur.

Data Synchronizer
An electronic circuit that uses a clock signal to synchronize data to facilitate interpretation.

Dedicated Landing Zone
The designated radial zone of the disk, usually at the inner portion of the disk, where the heads are stored to avoid contact with the data cylinders when power to the drive is off.

Defect Free
A term used to describe recording surfaces that have no detectable defects.

Defect Management
A general methodology of eliminating data errors on a recording surface by mapping out known defects on the media. The defective areas are rendered inaccessible, so that when information is written to the disk, it is stored to non-defective locations on the disk.

A personal computer sized to fit on or under your desktop. Western Digital EIDE hard drives are designed to fit into a desktop PC.

Differential SCSI
An electrical signal configuration which uses pairs of lines for data transfer. Used primarily in applications requiring long cable lengths of up to 82 feet (25 meters).

Direct Memory Access (DMA)
A process for transferring data directly to and from main memory, without passing through the CPU. DMA improves speed and efficiency by allowing the system to continue CPU processing even while it is transferring data to/from the hard drive.

A rigid platter, usually constructed of aluminum or mylar, with a magnetic surface that allows the recording of data, that is stored inside the drive.

Disk Controller
The chip or circuit that controls the transfer of data between the disk and buffer. (See also disk drive controller and interface controller).

Disk Drive Controller
The hard disk drive controller electronics which include the disk controller and the interface controller. (See also disk controller and interface controller.)

Disk Operating System (DOS)
The computer program that controls the organization of data, files and processes on the computer.

Disk Transfer Rate
Speed at which data transfers to and from the disk media (actual disk platter); a function of the recording frequency. Typical units are bits per second (BPS), or bytes per second. Hard drives have an increasing range of disk transfer rates from the inner diameter to the outer diameter of the disk.

Distribution Channel
Electronics distributors and certain retail chains that deliver electronic goods to end users through value-added resellers and some retail stores.