View source for Digital Linear Tape

{{short description|Magnetic tape-based data storage technology}}
{{Inline|date=September 2024}}
{{Infobox media
| name = Digital Linear Tape
| logo = 
| image = Super DLTtape I.jpg
| caption = A Super DLT I tape cartridge
| type = [[Magnetic tape cartridge]]
| encoding =
| capacity = 
| standard =
| owner = [[Digital Equipment Corporation]]
| manufacturer = 
| dimensions = 
| use = Data storage
| released = {{Start date and age|1984}}
}}
'''Digital Linear Tape''' ('''DLT'''; previously called '''CompacTape''') is a [[magnetic-tape data storage]] technology developed by [[Digital Equipment Corporation]] (DEC) from 1984 onwards. In 1994, the technology was purchased by [[Quantum Corporation]], who manufactured drives and licensed the technology and trademark. A variant with higher capacity is called '''Super DLT (SDLT)'''. The lower cost "value line" was initially manufactured by [[Benchmark Storage Innovations]] under license from Quantum. Quantum acquired Benchmark in 2002.

In 2007, Quantum stopped developing DLT drives, shifting its strategy to [[Linear Tape-Open|LTO]].

==History==
[[File:DEC-TK50-drive and cassette.jpg|thumb|upright=1.3|DEC TK50 drive and cartridge]]
[[File:Digital-compactape-ii hg.jpg|thumb|upright=.8|CompacTape II]]
[[File:Digital-compacttape hg.jpg|thumb|upright=.8|CompacTape III (DLT)]]
DEC launched the TK50 tape drive for the [[MicroVAX|MicroVAX II]] and [[PDP-11]] [[minicomputer]]s in 1984. This used 22-track CompacTape I cartridges, storing 94 MB per cartridge. The TK50 was superseded in 1987 by the TK70 drive and the 48-track CompacTape II cartridge, capable of storing 294 MB. In 1989, the CompacTape III (later DLTtape III) format was introduced, increasing the number of tracks to 128 and capacity to 2.6 GB. Later drives into the early 1990s improved the data density of the DLTtape III cartridge, up to 10 GB. The DLTtape IV cartridge was introduced by Quantum in 1994, with increased tape length and data density, initially offering 20 GB per tape. Super DLTtape, originally capable of up to 110 GB, was launched in 2001.

==Technology==
DLT uses [[Magnetic tape data storage#Linear|linear serpentine]] recording with multiple tracks on half-inch (12.7&nbsp;mm) wide tape. The [[Data cartridge (tape)|cartridges]] contain a single [[reel]] and the [[Magnetic tape|tape]] is pulled out of the cartridge by means of a leader tape attached to the take-up reel inside the drive. The drive leader tape is buckled to the cartridge leader during the load process. Tape speed and tension are controlled electronically via the reel motors; there is no [[Capstan (tape recorder) |capstan]]. The tape is guided by 4 to 6 rollers that touch only the back side of the tape. Tape material is [[metal particle tape]] (MP/AMP).

SDLT adds an [[Visual Servoing|optical servo]] system that reads servo patterns on the back of the tape to keep the data tracks on the front of the tape correctly aligned with the read/write heads. This is important for newer tape media, which have very thin, dense data tracks; 256, 384 and 768 data tracks on a {{convert |1/2|in|mm| adj=mid|-wide}} tape are available. 

DLT7000 and 8000 tilt the head forward and backward to reduce crosstalk between adjacent tracks through [[azimuth]]; this is called [[Symmetric Phase Recording]].

All (S)DLT drives support hardware [[data compression]]. The often-used compression factor of 2:1 is optimistic and generally only achievable for text data; a more realistic factor for a file system is 1.3:1 to 1.5:1, although drive compression applied to pre-compressed data can actually make the written data larger than having compression turned off in the tape drive.

Media are guaranteed for 30 years of [[data retention]] under specified environmental conditions; they are easily damaged by mishandling (dropping or improper packaging during shipment.)

Manufacturers of cartridges for the DLT/SDLT market are [[Fujifilm]], Hitachi/[[Maxell]] and [[Imation]]. VStape is made by [[Sony]]. All other companies/brands (even Quantum) are contractors and/or resellers of these companies.

A new naming convention took effect in 2005, calling the performance line DLT-S and the value line DLT-V.

DLT includes [[Write Once Read Many]] (WORM) capability.<ref>{{Citation | url = http://www.quantum.com/Products/TapeDrives/DLT/DLTSageWORM/ | title = DLTSage WORM functionality is available at no additional charge | publisher = Quantum}}.</ref>

In February 2007, Quantum stopped developing the next generations of DLT drives (S5 and V5) after insufficient market acceptance of the S4 and V4 drives, shifting its drive strategy to [[Linear Tape-Open|LTO]].

==Generations==
[[File:Supertape data storage capacities.svg|thumb|500px|Comparison of "supertape" capacities, including SDLT.]]
===Drives===
{| class="wikitable sortable"
!Drive
!Capacity (GB)
!Interface
!Data Rate (MB/s)
!Date
!Media
|-
|TK50/TZ30
|0.1
|proprietary/SCSI
|0.045
|1984
|CT I
|-
|TK70
|0.3
|proprietary
|0.045
|1987
|CT II
|-
|THZ01/DLT260/Tx85
|2.6
|[[Digital Storage Systems Interconnect|DSSI]]/[[SCSI]]
|0.8
|1991
|DLT III
|-
|THZ02/DLT600/Tx86
|6
|[[Digital Storage Systems Interconnect|DSSI]]/[[SCSI]]
|0.8
|1991
|DLT III
|-
|DLT2000/Tx87
|10
|Fast [[Parallel SCSI#SCSI-2|SCSI-2]]
|1.25
|1993
|DLT III
|-
|DLT2000XT
|15
|Fast [[Parallel SCSI#SCSI-2|SCSI-2]]
|1.25
|1995
|DLT IIIXT
|-
|DLT4000/Tx88
|20
|Fast [[Parallel SCSI#SCSI-2|SCSI-2]]
|1.5
|1994
|DLT IV
|-
|DLT7000/Tx89
|35
|Fast/Wide [[Parallel SCSI#SCSI-2|SCSI-2]]
|5
|1996
|DLT IV
|-
|DLT8000
|40
|Fast/Wide [[Parallel SCSI#SCSI-2|SCSI-2]]
|6
|1999
|DLT IV
|-
|SDLT 220
|110
|[[Parallel SCSI#Ultra-2|Ultra-2-Wide]] SCSI
|11
|1998
|SDLT I
|-
|SDLT 320
|160
|[[Parallel SCSI#Ultra-2|Ultra-2-Wide]] SCSI
|16
|2002
|SDLT I
|-
|SDLT 600
|300
|[[Parallel SCSI#Ultra-3|Ultra-160]] SCSI/[[Fibre Channel|FC]] 2Gb
|36
|2004
|SDLT II
|-
|SDLT 600A
|300
|[[Gigabit Ethernet|GbE]] ([[File Transfer Protocol|FTP]], [[HTTP]])
|36
|2005
|SDLT II
|-
|DLT-S4
|800
|[[Parallel SCSI#Ultra-320|Ultra-320]] SCSI/[[Fibre Channel|FC]] 4Gb/[[Serial Attached SCSI|SAS]]
|60
|2006
|S4
|-
|DLT-S4A
|800
|[[Gigabit Ethernet|GbE]] ([[File Transfer Protocol|FTP]], [[HTTP]])
|60
|2007
|S4
|-
| colspan=6 | Value line
|-
|DLT1
|40
|Fast/Wide [[Parallel SCSI#SCSI-2|SCSI-2]]
|3
|1999
|DLT IV
|-
|DLT-VS80
|40
|Fast/Wide [[Parallel SCSI#SCSI-2|SCSI-2]]
|3
|2001
|DLT IV
|-
|DLT-VS160
|80
|[[Parallel SCSI#Ultra-2|Ultra-2-Wide]] SCSI
|8
|2003
|VS1
|-
|DLT-V4
|160
|[[Parallel SCSI#Ultra-3|Ultra-160]] SCSI/[[Serial ATA|SATA]]/[[USB#USB_2.0|USB]]<ref>{{Citation | contribution-url = http://store.quantum.com/store/quantum/en_US/pd/productID.120423300/categoryID.18026400/parentCategoryID.18026300 | publisher = Quantum | title = Online Store | contribution =Product Info}}.</ref>
|10
|2005
|VS1
|}

===Media===
{| class="wikitable"
!Name
!Formats (GB)
!Colour
!Supported by (ro=read only)
|-
|CompacTape I
|0.1
|Light Grey
|TK50/TZ30, TK70 (ro)
|-
|CompacTape II
|0.3
|Dark Grey
|TK70
|-
|DLTtape III
|2.6, 6, 10
|Light brown
|DLT260/600, DLT2000/2000XT/4000/7000
|-
|DLTtape IIIXT
|15
|White
|DLT2000XT/4000/7000/8000
|-
|DLTtape IV
|20, 35, 40{{ref label|DLT-IV|a|a}}
|Dark brown
|DLT4000/7000/8000, DLT1/DLT-VS80{{ref label|DLT-IV|a|a}}, SDLT220/320 (ro)
|-
|Cleaning Tape III
|20 cleans
|Beige
|DLT2000/2000XT/4000/7000/8000
|-
|SDLTtape I
|110, 160
|Dark green
|SDLT220/320, SDLT600 (ro), DLT-S4 (ro)
|-
|SDLTtape II
|300
|Dark blue
|SDLT600, DLT-S4 (ro)
|-
|DLTtape S4
|800
|Dark purple
|DLT-S4
|-
|SDLT Cleaning Tape
|20 cleans
|Light grey
|SDLT220/320/600, DLT-S4
|-
|DLTtape VS1
|80, 160
|Ivory/Black
|VS160, DLT-V4, SDLT600 (ro)
|-
|DLT VS Cleaning Tape
|20 cleans
|Brown
|DLT1, DLT-VS80
|-
|DLT VS160 Cleaning Tape
|20 cleans
|Light grey
|DLT-VS160, DLT-V4
|}

{{note label|DLT-IV|a|a}} DLTtape IV can support both DLT4000/7000/8000 and DLT1/DLT-VS80 for full functions; once DLTtape IV media has been written to or formatted in a DLT7000/8000 drive, this media cannot be read, written to, or formatted in a DLT1/DLT-VS80 drive unless it is [[degaussing|degaussed]]. Once the media has been written to or formatted in a DLT4000 drive, the media cannot be written to or formatted in a DLT1/DLT-VS80 drive unless it is degaussed but it can be read. This is because the DLT1/VS series use a different recording format that is not fully supported by the other family.

Tapes written in value series drives can typically be read in (and often written to) higher end drives of a similar vintage, so long as the drive's technical specifications contain interoperability options.

==See also==
*[[Symmetric Phase Recording]]

==References==
{{Reflist |32em}}

==External links==
{{Commons category|Digital Linear Tape}}
* {{Citation | url = http://downloads.quantum.com/sdlt320/handbook.pdf | title = DLTtape Handbook | edition = 8th | publisher = Quantum | year = 2001 | format = [[Portable document format |PDF]] | access-date = 2005-10-26 | archive-date = 2014-07-29 | archive-url = https://web.archive.org/web/20140729065735/http://downloads.quantum.com/sdlt320/handbook.pdf | url-status = dead }}.
* {{usurped|1=[https://web.archive.org/web/20081015230507/http://www.dlttape.com/Roadmap/index.aspx DLT Roadmap (archived from 2006)]}} at {{usurped|1=[https://web.archive.org/web/20060615002922/http://www.dlttape.com/ dlttape.com]}}
* [http://www.thefreelibrary.com/DR.+FRED+HERTRICH+--+FATHER+OF+DLT.-a055867702 Obituary] of Dr. Fred Hertrich, "father" of DLT

===Standards===
* [http://www.ecma-international.org/publications/standards/Ecma-197.htm ECMA 197] Specification of DLT 2. [http://www.ecma-international.org/publications/files/ecma-st/ECMA-197.pdf]
* [http://www.ecma-international.org/publications/standards/Ecma-209.htm ECMA 209] Specification of DLT 3. [http://www.ecma-international.org/publications/files/ecma-st/ECMA-209.pdf]
* [http://www.ecma-international.org/publications/standards/Ecma-231.htm ECMA 231] Specification of DLT 4. [http://www.ecma-international.org/publications/files/ecma-st/ECMA-231.pdf]
* [http://www.ecma-international.org/publications/standards/Ecma-258.htm ECMA 258] Specification of DLT 3-XT. [http://www.ecma-international.org/publications/files/ecma-st/ECMA-258.pdf]
* [http://www.ecma-international.org/publications/standards/Ecma-259.htm ECMA 259] Specification of DLT 5. [http://www.ecma-international.org/publications/files/ecma-st/ECMA-259.pdf]
* [http://www.ecma-international.org/publications/standards/Ecma-286.htm ECMA 286] Specification of DLT 6. [http://www.ecma-international.org/publications/files/ecma-st/ECMA-286.pdf]
* [http://www.ecma-international.org/publications/standards/Ecma-320.htm ECMA 320] Specification of SDLT-1. [https://web.archive.org/web/20061008152758/http://www.ecma-international.org/publications/files/ECMA-ST/Ecma-320.pdf]

{{Magnetic tape data formats}}
{{Ecma International Standards}}
{{Digital Equipment Corporation}}

[[Category:DEC hardware]]
[[Category:Computer storage tape media]]
[[Category:Ecma standards]]
[[Category:Computer-related introductions in 1984]]