DAO
Disc-At-Once or DAO for CD-R media is a mode that masters the disc contents in one pass, rather than a track at a time as in Track At Once. DAO mode, unlike TAO mode, allows any amount of audio data (or no data at all) to be written in the "pre-gaps" between tracks.

Disc At Once recording for DVD-R media is a mode in which all data is written sequentially to the disc in one uninterrupted recording session. The on-disk contents result in a lead-in area, followed by the data, and closed by a lead-out area. The data is addressable in sectors of 2048 bytes each, with the first sector address being zero. There are no run-out blocks as in CD-R disc-at-once.

DAT
Digital Audio Tape. A 4mm wide tape used to record audio in digital form, usually by professional recording studios. Can be used to master compact discs from. A data version (DDS) is also available.

DDS
Digital Data Storage. A version of DAT used for storing computer data. Four types (DDS1, DDS2, DDS3 and DDS4) currently exist.

Decompression
To convert a compressed file or signal back into its original form before it was compressed.

Digital
A description of data which is stored or transmitted as a sequence of discrete symbols from a finite set, most commonly this means binary data represented using electronic or electromagnetic signals. (See also Analogue)

Disc
With a 'c' refers to CD, DVD, MiniDiscs and Laserdiscs.

Disc At Once (DAO)
Refers to the ability of certain CD-Recorders to record a CD-R or CD-RW disc in one continuous operation. This is the ideal mode in which to write CD masters being prepared for duplication/replication. (See also Track at Once).

Disk
With a 'k' refers to magnetic and magneto-optical disks (except MiniDisc).

DL
Dual Layer. This refers to a DVD recordable disc with 2 recording layers, one on top of the other - essentially a recordable version of the DVD-9 pressed disc.

DLT
Digital Linear Tape. The tape format used to transfer pre-mastered DVD data for glass mastering. Also used as high capacity storage for server and network backups.

Dual Disc
See DVDPlus

Duplication
A general industry term used to describe the low volume burning of CD and DVD recordable discs.

DVD
Digital Video Disc or Digital Versatile Disc depending upon who you listen to! It's a high capacity 'compact disc' that contains 7 times as much data as a standard CD on each of up to 4 layers.

DVD-5
A single-sided, single layer pre-recorded DVD disc format, with a capacity of 4.7 GB.

DVD-9
A single-sided, dual layer pre-recorded DVD disc format, with a capacity of 8.5 GB.

DVD-10
A double-sided pre-recorded DVD disc format, with a capacity of 9.4 GB.

DVD-18
A double-sided, dual layer pre-recorded DVD disc format, with a capacity of 17.1 GB. Very rare due to the difficult manufacturing processes involved.

DVD-Audio
A pre-recorded DVD format intended to carry high quality audio data plus optional images, text, video and menus. The format was defined in 1999 and players and discs appeared from late 2000.

DVD Authoring
The process of taking data assets such as video, audio, text, data and combining them into a DVD-Video or DVD-ROM compliant disc image. The inputs to this process might consist of compressed video files in MPEG2, compressed audio files in AC-3 and subtitles as bitmap images; the output or end result of the authoring process would typically be a DLT tape ready for DVD production.

DVD-ROM
A pre-recorded DVD disc, which includes the DVD-Audio and DVD-Video formats. Also used to describe other DVD formats not defined in the DVD specifications including PC/Mac applications and DVD based games consoles etc.

DVD-R
A recordable write-once DVD format, with a capacity of 4.7GB per side.

DVD-R DL
DVD-R DL (DL stands for Dual Layer), also called DVD-R9, is a derivative of the DVD-R format standard. DVD-R DL discs employ two recordable dye layers, each capable of storing nearly the 4.7 GB (4.38 GiB) of a single-layer disc, almost doubling the total disc capacity to 8.54 GB (7.96 GiB). Discs can be read in many DVD devices (older units are less compatible) and can only be written using DVD-R DL compatible recorders.

DVD-RW
A rewritable DVD with a capacity of 4.7 GB per side.

DVD+R
A recordable write-once format, developed to combat incompatibility issues between DVD-R/RW discs and home DVD video players. Not recognised by the DVDForum.

DVD+RW
A rewritable 12 cm optical disc with a capacity of 4.7GB per side. It is claimed to offer almost total compatibility with existing players, but is not an official DVD format.

DVD+R DL
DVD+R DL (DL stands for Dual Layer), also called DVD+R9, is a derivative of the DVD+R format created by the DVD+RW Alliance. Its use was first demonstrated in October 2003. DVD+R DL discs employ two recordable dye layers, each capable of storing nearly the 4.7 GB capacity of a single-layer disc, almost doubling the total disc capacity to 8.55 GB. Discs can be read in many DVD devices (older units are less compatible) and can only be created using DVD+R DL and Super Multi drives. DL drives started appearing on the market during mid 2004, at prices comparable to those of existing single-layer drives. However, the price of DL media ($1 to $5 USD per disc) is many times that of single-layer media. The latest DL drives write double layer discs at a slower rate (2.4x to 8x) than current single-layer media (8x-16x).

DVD-Video
A pre-recorded DVD format capable of carrying 133 minutes of high quality video (on a DVD-5) with multi-channel audio in up to 3 languages plus subtitles and menus to provide user interactivity. Other features include multiple camera angles, parental lock and random access.

DVDPlus
A double sided disc comprising a DVD substrate (with DVD-Video or DVD-Audio data) bonded to a CD substrate (containing CD audio). The CD substrate is usually about 0.9 mm thick so that the overall thickness is about 1.5 mm or less. An alternative name used by the major music companies is Dual Disc.

Dye
As a colour layer, the dye allows the recording of information onto a CD-R. During the process of recording the laser alters the organic features of the dye and creates the information structure. The resulting playback quality is similar to one of a pre-recorded CD or CD-ROM.