Glossary of PC terms: D

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Daisy chain	A way of connecting multiple internal drives to one PC controller. In this case, any signal from controller goes through  the drives and is received by the drive whose number matches. All drives have different numbers which are set using jumpers or switches.
Data loss / recovery	No technology is fail-safe to various unfortunate accidents that may happen at any time, leading to the disabling your storage system or damage to your storage media.  One thing to remember is that if the data are not physically destroyed (magnetic or optical bits are physically damaged), then there is always a chance to save them partially or completely. Otherwise, periodic data backup is the best protection against data loss. See also Data loss and Recovery.
Data transfer rate (DTR)	The speed at which bits of data are sent. For example, this could describe the rate at which the bits of information are read from the disk and sent to the drive's controller (internal rate), or characterize data exchange between the controller and PC's CPU (external rate).
Data compression	A process of data encoding based on locating and cutting out repeating data strings. When the data is read back, the cut out string is restored. Depending on the file format, some 80% of compression could be achieved. Other "denser" file formats will not benefit from compression at all.
Dedicated Servo System	Older drive design utilized a servo system which entirely used one side of one disk and one head. Modern drives usually use an Embedded Servo System.
Defragmentation of data	Different parts of the same file could be scattered all over the hard drive and this increases access time to this data.  Running Disk Defragmenter, which comes with Windows OS, will help to keep file fragmentation to a minimum.
Desktop drive	Modern desktop drives (1999 - beginning of 2000) usually come in a 3.5" form-factor, with one or few disk platters and twice as many MR (or GMR) magnetic heads, integrated drive electronics (IDE drives) or a separate controller card (SCSI drives), spin at 3,600 to 7,200 rpm, utilize CSS technology,  and provide the fastest data read / write among the non-solid-state-based storage devices.
Device Endpoint	A uniquely identifiable portion of a USB device that is the source or sink of information in a communication flow between the host and device.
Diskette	Floppy disk or floppy diskette. Today, a diskette usually is 3.5 inches in size and has a 1.44 MB storage capacity.
Digital tape	Magnetic tape optimized and used for storing data in a binary (digital) format.
Disk array	A linked group of small, independent drives used to replace larger, single disk drive systems and addressed by a computer as one unit. See also RAID.
Downstream	The direction of data flow away from the host.
DMA	Direct memory access.  A technology designed to speed up data exchange between computer peripherals and the RAM by avoiding CPU-imposed delays. See also ATA-2.
Drive utilities	A set of programs used to optimize drive performance (Disk Defragmenter, Speed Disk, etc.), to increase drive capacity (Compression Agent, etc.), recover errors or media damage (Disk Scan, CHKDSK, etc.), or to simplify or make possible drive installation (EZ-DRIVE, etc.). Go here for examples.
Driver	A small program responsible for interfacing to a hardware device.

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