Data Recovery and Digital Storage Glossary

• DAE
  Digital Audio Extraction.
  
  
• Data Recovery
  The salvaging of data stored on damaged media, such as magnetic disks and tapes. Of course, not all data is recoverable, but data recovery specialists can often restore a surprisingly high percentage of the data on damaged media.
  
  
• Disc-At-Once
  A method of recording CDs where, the entire CD is recorded in one pass without turning off the laser. Disc-At-Once allows you to run tracks together without a pause (songs on a CD-DA disc can run together).
  
  
• Disc Image
  A file that contains all of the data needed to create a CD. Disc images can be mounted and browsed like any other volume.
  
  
• DMA
  Direct Memory Access. A mode of data transfer. DMA accelerates transfer rates because it does not access the computer's processor. Ultra DMA can support two devices and transfer data at rates up to either 33 MB/s or 66 MB/s depending on the type of Ultra DMA bus.
  
  
• DVD Specifications
  The specifications for Digital Versatile Disc are contained in several books. Historically, these books were listed as Books A–E. Currently, they are referred to by the name of the format they describe. I.e., Book A which discusses the DVD-ROM format is now called the DVD-ROM book. The DVD specifications are listed below by their old names:
  
  
  • Book A
    DVD specification that describes the DVD-ROM format.
    
    
  • Book B
    DVD specification that describes the DVD-Video format.
    
    
  • Book C
    DVD specification that describes the DVD-Audio format. This specification has not been finalized.
    
    
  • Book D
    DVD specification that describes the DVD-R format.
    
    
  • Book E
    DVD specification that describes the DVD-ReWritable format.
    
    
• DVD-Audio
  Digital Versatile Disc-Audio. Digital Versatile Disc will eventually be used to distribute music much like today's Compact Discs. The specifications for DVD-Audio have not yet been finalized. The initial DVD-Audio specification is based on the Red Book CD-DA specification (44.1 kHz, 16-bit samples). The finalized specification should add at least two other audio specifications: 48 kHz, 20-bit samples, 8 channels, 96 minutes per layer and 96 kHz, 16-bit samples, 8 channels, 86 minutes per layer.
  
  
• DVD
  Digital Versatile Disc or Digital Video Disc. DVD (Digital Versatile Disc or Digital Video Disc) is an emerging standard for storing video, audio, and data files that has been embraced by both the computer and home entertainment industries. DVD allows up to 17GB of data on a single CD-sized disc
  many times more data than the 650 MB stored on a standard CD. DVDs can be either single or double sided and contain more than one layer per side. A single-sided, single-layered DVD can hold 4.7GB or about 2 hours of high quality video; however, a double-sided, double-layered DVD can hold 17GB or about 8 hours of high quality video.
  
  
  • Single-Sided, Single-Layered 4.7 GB 2 hrs video
    
    
  • Single-Sided, Double-Layered 8.5 GB 4 hrs video
    
    
  • Double-Sided, Single-Layered 9.4 GB 4 hrs video
    
    
  • Double-Sided, Double-Layered 17 GB 8 hrs video
    
    
• DVD-ER
  see DVD-RW.
  
  
• DVD-RAM
  Digital Versatile Disc-Random Access Memory. One of three competing formats for the DVD-ReWritable standard. A rewritable DVD based on Book E of the DVD specifications. DVD-RAM initially held up to 2.66 GB of data; however, the DVD-RAM 2.0 specification changed the capacity to 4.7 GB. DVD-RAM was developed by Hitachi and Matsushita. The current DVD-RAM specification does not include double-layered discs. See DVD-ReWritable.
  
  
• DVD-R
  Digital Versatile Disc-Recordable. A recordable DVD based on the Book D specification and designed to eventually replace CD-R. DVD-R can hold 4.7 GB of data per side. The current DVD-R specification does not include double-layered discs.
  
  
• DVD+R
  Digital Versatile Disc+Recordable. One of two competing formats for the DVD recordable standard designed to eventually replace CD-R. DVD+R was developed by Philips, Sony, and Hewlett-Packard. DVD+R can hold 4.7 GB of data per side.
  
  
• DVD-ReWritable
  Digital Versatile Disc-ReWritable. There are currently three different formats competing to become the standard for rewritable DVDs: DVD-RAM, DVD-RW, and DVD+RW. All of the DVD-ReWritable formats are capable of rewriting a disc at least 1,000 times. DVD-ReWritable media is not currently readable in many home DVD players.
  
  
• DVD-ROM
  Digital Versatile Disc-Read Only Memory. A DVD used to store computer data. Data cannot be written to a DVD-ROM. DVD-ROM is described in Book A of the DVD specification.
  
  
• DVD-R/W, DVD-RW
  Digital Versatile Disc-ReWritable (formerly DVD-R/W or DVD-ER). One of three competing formats for the DVD-ReWritable standard. DVD-RW was developed by Pioneer and is based on the DVD-R mechanism. DVD-RW can hold at least 4.7 GB of data per side. See DVD-ReWritable.
  
  
• DVD+RW
  Digital Versatile Disc+ReWritable. One of three competing formats for the DVD-ReWritable standard. DVD+RW was developed by Philips, Sony, and Hewlett-Packard. DVD+RW can hold at least 4.7 GB of data per side. See DVD-ReWritable.
  
  
• DVD-Video
  Digital Versatile Disc-Video. A single-sided, single-layered DVD-Video can contain 133 minutes of high quality full motion MPEG-2 video and audio (NTSC: 720 x 480 @ 30 frames/sec. PAL: 720 x 576 @ 25 frames/sec). DVD-Video commonly offers language selection, interactive menus, regional encoding and copy protection.