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Digital Linear Tape

A Super DLT I tape cartridge
Media type	Magnetic tape cartridge
Developed by	Digital Equipment Corporation
Usage	Data storage
Released	1984; 42 years ago (1984)

Digital Linear Tape (DLT; previously calledCompacTape) is amagnetic-tape data storage technology developed byDigital Equipment Corporation (DEC) from 1984 onwards. In 1994, the technology was purchased byQuantum Corporation, who manufactured drives and licensed the technology and trademark. A variant with higher capacity is calledSuper DLT (SDLT). The lower cost "value line" was initially manufactured byBenchmark Storage Innovations under license from Quantum. Quantum acquired Benchmark in 2002.

In 2007, Quantum stopped developing DLT drives, shifting its strategy toLTO.

DEC launched the TK50 tape drive for theMicroVAX II andPDP-11minicomputers 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 The TK50 was superseded in 1987 by the TK70 drive and the 48-track CompacTape II cartridge, capable of storing 294 MB.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.

DLT useslinear serpentine recording with multiple tracks on half-inch (12.7 mm) wide tape. Thecartridges contain a singlereel and thetape 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 nocapstan. The tape is guided by 4 to 6 rollers that touch only the back side of the tape. Tape material ismetal particle tape (MP/AMP).

SDLT adds anoptical 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 a1⁄2-inch-wide (13 mm) tape are available.

DLT7000 and 8000 tilt the head forward and backward to reduce crosstalk between adjacent tracks throughazimuth; this is calledSymmetric Phase Recording.

All (S)DLT drives support hardwaredata 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 ofdata 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 areFujifilm, Hitachi/Maxell andImation. VStape is made bySony. 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 includesWrite Once Read Many (WORM) capability.^[1]

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 toLTO.

^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 isdegaussed. 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.

• Symmetric Phase Recording

Wikimedia Commons has media related toDigital Linear Tape.

• DLTtape Handbook(PDF) (8th ed.), Quantum, 2001, archived fromthe original(PDF) on 2014-07-29, retrieved2005-10-26.
• DLT Roadmap (archived from 2006) atdlttape.com
• Obituary of Dr. Fred Hertrich, "father" of DLT

• ECMA 197 Specification of DLT 2.[1]
• ECMA 209 Specification of DLT 3.[2]
• ECMA 231 Specification of DLT 4.[3]
• ECMA 258 Specification of DLT 3-XT.[4]
• ECMA 259 Specification of DLT 5.[5]
• ECMA 286 Specification of DLT 6.[6]
• ECMA 320 Specification of SDLT-1.[7]

• DEC hardware
• Computer storage tape media
• Ecma standards
• Computer-related introductions in 1984

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