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Digital Data Storage is a format for storing computer
Computer
A computer is a programmable machine designed to sequentially and automatically carry out a sequence of arithmetic or logical operations. The particular sequence of operations can be changed readily, allowing the computer to solve more than one kind of problem...

 data
Data
The term data refers to qualitative or quantitative attributes of a variable or set of variables. Data are typically the results of measurements and can be the basis of graphs, images, or observations of a set of variables. Data are often viewed as the lowest level of abstraction from which...

 on a Digital Audio Tape
Digital Audio Tape
Digital Audio Tape is a signal recording and playback medium developed by Sony and introduced in 1987. In appearance it is similar to a compact audio cassette, using 4 mm magnetic tape enclosed in a protective shell, but is roughly half the size at 73 mm × 54 mm × 10.5 mm. As...

 (DAT).

DDS uses tape with a width of 3.8mm, with the exception of the latest formats, DAT 160 and DAT 320, which are 8mm wide. Initially, the tape was 60 or 90 meters 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 scan
Helical scan is a method of recording high bandwidth signals onto magnetic tape. It is used in reel-to-reel video tape recorders, video cassette recorders, digital audio tape recorders, and some computer tape drives....

ning for recording, the same process used by a video cassette recorder (VCR). If errors are present, the write heads rewrite the data.

Tape drives should be cleaned regularly to be kept in good working order.

Backward compatibility between newer drives and older tapes is not assured. See HP's compatibility matrix: 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 LTO
Linear Tape-Open
Linear Tape-Open is a magnetic tape data storage technology originally developed in the late 1990s as an open standards alternative to the proprietary magnetic tape formats that were available at the time. Hewlett-Packard, IBM and Seagate initiated the LTO Consortium, which directs development...

, AIT
Advanced Intelligent Tape
Advanced Intelligent Tape is a discontinued high-speed, high-capacity magnetic tape data storage format developed and controlled by Sony. It competed mainly against the DLT, LTO, DAT/DDS, and VXA formats. AIT uses a cassette similar to Video8. Super AIT is a higher capacity variant using wider...

, VXA
VXA
VXA is a tape backup format originally created by Ecrix and now owned by Tandberg Data. After the merger between Ecrix and Exabyte, VXA was produced by Exabyte Corporation...

, and Travan
Travan
Travan is an 8 mm magnetic tape cartridge design developed by the 3M company, used for the storage of data in computer backups and mass storage. Over time, subsequent versions of Travan cartridges and drives have been developed that provide greater data capacity, while retaining the standard 8 mm...

 formats.

Generations

Format Date Tape Width
(mm)		 Tape Length
(m)		 Capacity
(GB)		 Speed
(MB/s)
DDS-1 1989 3.81 60/90 1.3/2.0 0.18
DDS-2 1993 3.81 120 4.0 0.6
DDS-3 1996 3.81 125 12.0 1.1
DDS-4 1999 3.81 150 20.0 3.2
DAT-72 2003 3.81 170 36.0 3.2
DAT-160 2007 8 154 80 6.9
DAT-320 2009 8 160 12
Gen 8 TBA 8 ~300 >16

DDS-1

Stores up to 1.3 GB uncompressed (2.6 GB compressed) on a 60 m cartridge, 2 GB uncompressed (4 GB compressed) on a 90 m cartridge.

The DDS-1 Cartridge often does not have the -1 designation. It can often be recognized by having 4 vertical bars separated from DDS by the words e "Digital Data Storage"..

DDS-3

Stores up to 12 GB uncompressed (24 GB compressed) on a 125 m cartridge. DDS-3 uses PRML (Partial Response Maximum Likelihood)
PRML
In computer data storage, Partial Response Maximum Likelihood is a method for converting the weak analog signal from the head of a magnetic disk or tape drive into a digital signal. PRML attempts to correctly interpret even small changes in the analog signal, whereas peak detection relies on fixed...

. PRML minimizes 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
Certance
Certance was a computer tape drive manufacturer based in Costa Mesa, California. Certance made DDS tape drives and was one of the three original technology partners that created the Linear Tape-Open technology. In 2005 Certance was acquired by Quantum Corp....

. It has the same form-factor and is backwards compatible with DDS-3 and -4.


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 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
SCSI
Small Computer System Interface is a set of standards for physically connecting and transferring data between computers and peripheral devices. The SCSI standards define commands, protocols, and electrical and optical interfaces. SCSI is most commonly used for hard disks and tape drives, but it...

 and USB, with SAS interface now released.

DAT 320

In November 2009 HP launched the new DAT 320 which stores up to 160 GB uncompressed (marketed as 320 GB assuming 2:1 compression).

Future

About two years after DAT 320 the next format is planned to be launched, storing approximately 300 GB uncompressed.

Official standards


External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
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