Digital Data Storage
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2008-07-02T23:07:46Z
Mild Bill Hiccup
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{{this2|a particular data storage media|the general meaning|data storage device}}
[[Image:DDS-logo.png|right]]
'''Digital Data Storage''' ('''DDS''') is a format for storing and [[backup|backing]] up [[computer]] [[data]] on [[magnetic tape]] that evolved from [[Digital Audio Tape]] (DAT) technology, which was originally created for [[compact disc|CD]]-quality audio recording. In 1989, [[Sony]] and [[Hewlett Packard]] defined the DDS format for data storage using DAT tape cartridges. Tapes conforming to the initial DDS format can be "played" by either DAT or DDS tape machines. However, most DDS tape drives cannot retrieve the audio stored on a DAT cartridge.
DDS uses 3.8 [[millimeter]] wide tape. Initially, the tape was 60 or 90 [[meter]]s long, although advancements in materials technology have allowed the length to be increased significantly in successive versions. A DDS tape drive uses [[Helical scan|helical scanning]] for recording, the same process used by a [[video cassette recorder]] (VCR). There are two read heads and two write heads. The read heads verify the data that has been written (recorded). If errors are present, the write heads rewrite the data.
A DDS cartridge needs to be retired after 2,000 passes or 100 full backups. Tape drives should be cleaned regularly to be kept in good working order. DDS tapes have an expected life of at least 10 years.
Backward compatibility between newer drives and older tapes is not assured. See HP's compatibility matrix: [http://h20000.www2.hp.com/bizsupport/TechSupport/Document.jsp?objectID=lpg50457&locale=en_US&taskId=101&prodSeriesId=81997&prodTypeId=12169 Compatibility Matrix]
Notice in HP's article that newer tape standards do not simply consist of longer tapes. For example, the track is narrower in DDS2 than in DDS1.
The DDS format competes mainly against the [[Linear Tape-Open|LTO]], [[Advanced Intelligent Tape|AIT]], [[VXA]], and [[Travan]] formats.
[[Image:DDS2 tape with scale.jpg|thumb|A DDS-2/DAT cassette]]
== Generations ==
{| class="wikitable" style="float:right; margin-left: 1em;"
|- bgcolor="#cccccc"
! Format
! Date
! abbr="Length" | Tape Length (m)
! abbr="Capacity" | Capacity (GB)
! abbr="Speed" | Speed (MB/s)
|-
!DDS-1
|1989
|60/90
|1.3/2.0
|0.6
|-
!DDS-2
|1993
|120
|4.0
|0.6
|-
!DDS-3
|1996
|125
|12.0
|1.1
|-
!DDS-4
|1999
|150
|20.0
|3.2
|-
!DAT 72
|2003
|170
|36.0
|3.2
|-
!DAT 160
|2007
|150
|80
|6.9
|}
=== DDS-1 ===
Stores up to 1.3 GB uncompressed (2.6 GB compressed) on a 60 meter cartridge, 2 GB uncompressed (4 GB compressed) on a 90 meter cartridge.
=== DDS-2 ===
Stores up to 4 GB uncompressed (8 GB compressed) on a 120 meter cartridge.
=== DDS-3 ===
Stores up to 12 GB uncompressed (24 GB compressed) on a 125 meter cartridge. DDS-3 uses PRML (Partial Response Maximum Likelihood). PRML eliminates electronic noise for a cleaner data recording.
=== DDS-4 ===
DDS-4 stores up to 20 GB uncompressed (40 GB compressed) on a 150 meter cartridge. This format is also called DAT 40.
[[Image:DAT72-logo.png|right]]
=== DAT 72 ===
DAT72 stores up to 36 GB uncompressed (72 GB compressed) on a 170 meter cartridge. The DAT 72 standard was developed by HP and [[Certance]]. It has the same form-factor and is backwards compatible with DDS-3 and -4.
[[Image:DAT160-logo.png|right]]
=== DAT 160 ===
DAT 160 was launched in June 2007 by HP. A major change from the previous generations is the width of the tape. DAT 160 uses 8 mm wide tape while all prior versions use 3.81 mm wide tape. Despite the difference in tape widths, DAT 160 drives are backwards compatible with DAT 72 and DAT 40 (DDS-4). Native capacity is 80 GB and native transfer rate 6.9 MB/s. Launch interfaces are SCSI and USB.
The next drive in the DAT roadmap is the DAT 320.
== Official standards ==
* [http://www.ecma-international.org/publications/standards/ECMA-139.htm ECMA-139] ''ISO/IEC 10777:1991'', Specification of '''DDS'''. [http://www.ecma-international.org/publications/files/ecma-st/ECMA-139.pdf]
* [http://www.ecma-international.org/publications/standards/ECMA-146.htm ECMA-146] ''ISO/IEC 11321:1992'', Specification of '''DATA/DAT'''. [http://www.ecma-international.org/publications/files/ecma-st/ECMA-146.pdf]
* [http://www.ecma-international.org/publications/standards/ECMA-150.htm ECMA-150] ''ISO/IEC 11557:1992'', Specification of '''DDS-DC''' (DDS w/ compression). [http://www.ecma-international.org/publications/files/ecma-st/ECMA-150.pdf]
* [http://www.ecma-international.org/publications/standards/ECMA-151.htm ECMA-151] ''ISO/IEC 11558:1992'', Specification of '''DCLZ''' (compression algorithm). [http://www.ecma-international.org/publications/files/ecma-st/ECMA-151.pdf]
* [http://www.ecma-international.org/publications/standards/ECMA-170.htm ECMA-170] ''ISO/IEC 12447:1993'', Specification of '''DDS''' (for 60m and 90m tapes). [http://www.ecma-international.org/publications/files/ecma-st/ECMA-170.pdf]
* [http://www.ecma-international.org/publications/standards/ECMA-171.htm ECMA-171] ''ISO/IEC 12448:1993'', Specification of '''DATA/DAT-DC''' (for 60m and 90m tapes). [http://www.ecma-international.org/publications/files/ecma-st/ECMA-171.pdf]
* [http://www.ecma-international.org/publications/standards/ECMA-198.htm ECMA-198] ''ISO/IEC 13923'', Specification of '''DDS-2'''. [http://www.ecma-international.org/publications/files/ecma-st/ECMA-198.pdf]
* [http://www.ecma-international.org/publications/standards/ECMA-236.htm ECMA-236] ''ISO/IEC 15521'', Specification of '''DDS-3'''. [http://www.ecma-international.org/publications/files/ecma-st/ECMA-236.pdf]
* [http://www.ecma-international.org/publications/standards/Ecma-288.htm ECMA-288] ''ISO/IEC 17462'', Specification of '''DDS-4'''. [http://www.ecma-international.org/publications/files/ecma-st/ECMA-288.pdf]
==External links==
* [http://www.datmgm.com/ DAT Manufacturers Group]
{{Magnetic_tape_data_formats}}
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[[Category:Computer storage tape media]]
[[Category:Computer storage devices]]