Glossary of Western Digital Hard Disk Drive (Letter D)

Data Lifeguard Tools™
A set of software utilities that work in conjunction with embedded Data Lifeguard features to make hard drive installation, drive management diagnostics, and repair simple and worry-free.

Data Lifeguard™
A WD-exclusive data reliability feature that automatically detects, isolates, and repairs problem areas on a hard drive and prevents data loss.

data synchronizer
An electronic circuit that uses a clock signal to synchronize data.

data transfer rate
The rate that digital data transfers from one point to another, expressed in bits per second or bytes per second. Data transfer rate to disk (internal disk transfer rate) is expressed in megabits per second (Mb/s). Data transfer rate from buffer to host (transfer of buffered data) is expressed in megabytes per second (MB/s).

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.

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

defect free
A term to describe recording surfaces that have no detectable defects.

defect management
A general method of eliminating data errors on a recording surface by mapping out known media defects. Defective areas are rendered inaccessible, so that subsequent operations write data only to non-defective locations.

A personal computer sized to fit on or under your desktop. WD internal hard drives are designed to fit into a desktop PC.

Dynamic host configuration protocol. A protocol for assigning IP addresses to devices on a network. With dynamic addressing, a device can have a different IP address each time it connects to the network. In some systems, the device’s IP address even changes while it is still connected. DHCP also supports a mix of static and dynamic IP addresses.

differential SCSI
An electrical signal configuration that uses pairs of lines for data transfer, primarily in applications requiring cable lengths up to 82 feet (25 meters).

A rigid platter, usually constructed of aluminum or Mylar® and with a magnetic surface that allows the recording of data.

disk controller
A chip or circuit that controls data transfers between disk and buffer. See also disk drive controller and interface controller.

disk drive controller
Hard disk drive controller electronics, which include the disk controller and interface controller. See also disk controller and interface controller.

disk transfer rate
Speed at which data is transferred to/from disk (platter); a function of the recording frequency. Typical units are bits per second (b/s), or bytes per second (B/s). A hard drive disk transfer rate increases from the inner diameter to the outer diameter of the disk.

distribution channel
Electronics distributors and retail chains that deliver electronic goods to end users through value-added resellers and retail stores.

Digital Living Network Alliance. The group of consumer electronics, computing industry, and mobile device companies that sets standards for product compatibility, thus enabling users to share content in their home.

Digital Media Adapter. A device that gives home entertainment devices the ability to transfer media such as music, photos, and videos to and from other devices over the network.

Direct memory access. A process that transfers data directly to/from main memory, without passing through a CPU. DMA improves speed and efficiency by allowing a system to continue CPU processing while transferring data to/from a hard drive.

Domain Name Service. A system that allows a network name server to translate text host names into numeric IP addresses used to uniquely identify any device connected to the Internet.

Disk Operating System. A 16-bit operating system developed by Microsoft that was formerly the standard operating system for IBM-compatible PCs. DOS does not support multiple users or multitasking.

Data Path Protection. A feature that prevents possible electronic failures by preventing corruption of data on the hard drive.

Dual Stage Actuator. DSA is an improvement to the overall capability of the Servo system. It provides a mechanical benefit to improve the response time (higher bandwidth capability) of moving and maintaining the head position over the media.

dual interface
An external storage device with two interfaces available for connection to the computer.

dual-option backup
The ability to back up a drive either manually (on demand) or automatically.

DuraStep Ramp™
WD technology that locks the heads of a data disk to provide additional shock protection.

duty cycle
The time a component, device, or system is actually operating as compared to the time it is powered on; can be expressed as a ratio or percentage.

Digital video recorder.