View source for Digital Data Storage

{{short description|Computer data storage technology based on magnetic tape}}
{{About|a particular technology|the general concept|Computer data storage}}
{{refimprove|date=February 2013}}
{{context|date=August 2021}}
{{Infobox storage medium
| name          = Digital Audio Tape
| logo          = Digital Data Storage logo.svg{{!}}class=skin-invert
| image         = 
| caption       = 
| type          = [[Magnetic cassette tape]]
| encoding      = Lossless real-time
| capacity      = 
| read          = Rotating head
| write         = Rotating head, helical scan
| standard      =
| owner         = [[Sony]]
| use           = Data storage
| extended from = [[Digital Audio Tape]]
| extended to   = 
| released      = {{Start date and age|1989}}
}}

'''Digital Data Storage''' ('''DDS''') is a [[computer]] [[data]] storage technology that is based upon the [[Digital Audio Tape]] (DAT) format that was developed during the 1980s.  DDS is primarily intended for use as off-line storage, especially for generating [[backup|backup copies]] of working data.

== Design ==
A DDS cartridge uses tape with a width of 3.81mm, with the exception of the latest formats, DAT-160 and DAT-320, both which use 8mm wide tape.  Initially, the tape was 60 meters (197 feet) or 90 meters (295&nbsp;ft.) in length. Advancements in materials technology have allowed the length to be increased significantly in successive versions.  A DDS tape drive uses [[helical scan]] recording, the same process used by a [[video cassette recorder]] (VCR).

Backward compatibility between newer drives and older cartridges is not assured; the compatibility matrices provided by manufacturers will need to be consulted.<ref>Compatibility matrix for: [http://h20564.www2.hpe.com/hpsc/doc/public/display?docId=emr_na-lpg50457 HP], [https://www.ibm.com/support/knowledgecenter/en/ssw_ibm_i_72/rzam4/rzam4datcompat.htm IBM]</ref>  Typically drives can read and write tapes in the prior generation format, with most (but not all) also able to read and write tapes from two generations prior.  Notice in HP's article that newer tape standards do not simply consist of longer tapes; with DDS-2, for example, the track was narrower than with DDS-1.

At one time, DDS competed against the [[Linear Tape-Open]] (LTO), [[Advanced Intelligent Tape]] (AIT), [[VXA]], and [[Travan]] formats. However, AIT, Travan and VXA are no longer mainstream, and the capacity of LTO has far exceeded that of the most recent DDS standard, DDS-320.

== History ==
{{proseline|section|date=August 2021}}
[[File:DDS2 tape with scale.jpg|thumb|A DDS-2 cartridge.]]
[[File:DDS Streamer inside.jpg|thumb|DDS Streamer inside]]
[[File:DDS4 Cartritge IMG 8918.jpg|thumb|DDS Cartridges]]
[[File:HP Tape.jpg|thumb|A DAT 72 cartridge]]
[[File:DAT 160 logo.svg|thumb|DAT 160 logo]]
[[File:DAT 72 Tape Drive Front, Wiki, EN.jpg|thumb|DAT-72 tape drive, front panel]]

; DDS-1: Stores up to 1.3 GB uncompressed (2.6 GB [[Data compression|compressed]]) on a 60 m cartridge or 2 GB uncompressed (4 GB compressed) on a 90 m cartridge. The DDS-1 cartridge often does not have the -1 designation, as initially it was the only format, though cartridges produced since the introduction of DDS-2 may carry a -1 designation to distinguish the format from newer formats. A media recognition system was introduced with DDS-2 drives and cartridges to detect the medium type and prevent the loading of an improper medium. From 1993, DDS-1 tapes included the media recognition system marks on the leader tape&mdash;a feature indicated by the presence of four vertical bars after the DDS logo.
; DDS-2: Stores up to 4 GB uncompressed (8 GB compressed) on a 120 m cartridge.
; DDS-3: Stores up to 12 GB uncompressed (24 GB compressed) on a 125 m cartridge. DDS-3 uses [[PRML|PRML (Partial Response Maximum Likelihood)]] to minimize electronic noise for a cleaner data recording.
; DDS-4: DDS-4 stores up to 20 GB uncompressed (40 GB compressed) on a 150 m cartridge. This format is also called DAT 40.
; DAT 72: DAT 72 stores up to 36 GB uncompressed (72 GB compressed) on a 170 m cartridge. The DAT 72 standard was developed by HP and [[Certance]]. It has the same form-factor as DDS-3 and -4 and is sometimes referred to as DDS-5.
; DAT 160: DAT 160 was launched in June 2007 by HP, stores up to 80 GB uncompressed (160 GB compressed). A major change from the previous generations is the width of the tape. DAT 160 uses 8&nbsp;mm wide tape in a slightly thicker cartridge while all prior versions use 3.81&nbsp;mm wide tape. Despite the difference in tape widths, DAT 160 drives can load DAT-72 and DAT-40 (DDS-4) cartridges. Native capacity is 80 GB and native transfer rate was raised to 6.9 MB/s, mostly due to prolonging head/tape contact to 180° (compared to 90° previously).<ref>{{cite web|url=http://www.dat-mgm.com/about |title=DAT Technology |access-date=2013-03-31 |publisher=DAT Manufacturers Group |url-status=bot: unknown |archive-url=https://web.archive.org/web/20130531190032/http://www.dat-mgm.com/about%20DAT/DAT%20technology/ |archive-date=2013-05-31 }}</ref> Launch interfaces were [[Parallel SCSI]] and [[USB]], with [[Serial Attached SCSI|SAS]] interface released later.
; DAT 320: In November 2009 HP announced the DAT-320 standard, which stores up to 160 GB uncompressed (marketed as 320 GB assuming 2:1 compression) per cartridge. Native transfer rate was raised to 12 MB/s.

=== Generations ===
{| class="wikitable" style="text-align:right"
|+ DDS generations
! Format
! Date
! abbr="Width" | Tape<br />width<br/>(mm)
! abbr="Track" | Track<br />pitch<br />(μm)
! abbr="Length" | Tape<br />length<br />(m)
! abbr="Capacity" | Native<br />capacity<br />(GB)
! abbr="Compressed" | Capacity assuming<br />2:1 compression<br>(GB)
! abbr="RPM" | Drum rotation<br />speed<br />(RPM)
! abbr="Speed" | Data transfer<br />speed<br />(MB/s)
|-
! DDS-1
| 1989
| 3.81
| 13.6
| 60/90
| 1.3/2.0
| 2.6/4
| 2000, 2551
| 0.183
|-
! DDS-2
| 1993
| 3.81
| 9.1
| 120
| 4.0
| 8
| 4000, 4400, 5737, 8500
| 0.360-0.720
|-
! DDS-3
| 1996
| 3.81
| 9.1
| 125
| 12.0
| 24
| 3825, 4252
| <1.5
|-
! DDS-4
| 1999
| 3.81
| 6.8
| 150
| 20.0
| 40
| 11400
| 1.0-3.2
|-
! DAT-72
| 2003
| 3.81
| 5.4
| 170
| 36.0
| 72
| 8609.7, 10000
| 3.2
|-
! DAT-160
| 2007
| 8
| 6.8
| 154
| 80
| 160
| 6457
| 6.9
|-
! DAT-320
| 2009
| 8
|
| 153<ref>{{cite web |url= http://h30094.www3.hp.com/product/sku/10209877/mfg_partno/Q2032A |title= HP DAT 320 320GB Data Cartridge - DAT & DDS tape cartridges - HP: Q2032A |publisher= Hewlett-Packard |access-date= 2013-12-31 |archive-url= https://web.archive.org/web/20140101091210/http://h30094.www3.hp.com/product/sku/10209877/mfg_partno/Q2032A |archive-date= 2014-01-01 |url-status= dead }}</ref>
| 160
| 320
|
| 12
|-
! (Gen 8)
| canceled
| 8
|
|
| ~300
| ~600
|
| ≥16
|}

=== Future ===
The next format, Gen 8, was canceled.{{cn|date=October 2022}}

== See also ==
* [[Data8]]
* [[Magnetic storage]]

== References ==
{{refs}}

== External links ==
{{commonscat|Digital Data Storage}}

* [https://web.archive.org/web/20130531190032/http://dat-mgm.com/ DAT Manufacturers Group]
* [https://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 ECMA-139]
* [https://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 ECMA-146]
* [https://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 ECMA-150]
* [https://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 ECMA-151]
* [https://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 ECMA-170]
* [https://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 ECMA-171]
* [https://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 ECMA-198]
* [https://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 ECMA-236]
* [https://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 ECMA-288]

{{Magnetic tape data formats}}
{{Ecma International Standards}}

[[Category:Computer storage tape media]]
[[Category:Computer file formats]]