Digital Data Storage

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Digital Data Storage (DDS) is a format for storing and backing up computer data on magnetic tape that evolved from Digital Audio Tape (DAT) technology, which was originally created for 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 meters long, although advancements in materials technology have allowed the length to be increased significantly in successive versions. A DDS tape drive uses 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.

The DDS format competes mainly against the AIT, VXA, and Travan formats.

Contents 1 Generations 1.1 DDS-1 1.2 DDS-2 1.3 DDS-3 1.4 DDS-4 1.5 DAT 72 1.6 DAT 160 2 External links

[edit] Generations

Format	Date	Tape Length (m)	Capacity (GB)	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	2.4
DAT 72	2003	170	36.0	3.5
DAT 160	2006	N/A	N/A	N/A

[edit] DDS-1

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

[edit] DDS-2

Stores up to 4 GB uncompressed (8 GB compressed) on a 120 meter cartridge.

[edit] 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.

[edit] DDS-4

DDS-4 stores up to 20 GB uncompressed (40 GB compressed) on a 150 meter cartridge.

[edit] 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. The data transfer rate was hoped to be around 7 MB/s.

[edit] DAT 160

HP was asked if the DAT 160 schedule is on track for the end of the year. Chris Sopp, HP's European tape product marketing manager, said DAT 160 will arrive in the first three months of 2006. It will use a wider tape than DAT 72 but drives will be able to read DAT 72 tapes because there will be two load mechanisms. It will also have a USB connection as well as a parallel SCSI one.

He said that it was possible the next DAT drive, the DAT 320, will have a serial-attached SCSI (SAS) connection when it arrives.

[edit] External links

• DAT Manufacturers Group
• Using Audio DATs in DDS drives
• A brief history of tape (pdf)
• ECMA-139 ISO/IEC 10777:1991, Specification of DDS. [1]
• ECMA-146 ISO/IEC 11321:1992, Specification of DATA/DAT. [2]
• ECMA-150 ISO/IEC 11557:1992, Specification of DDS-DC (DDS w/ compression). [3]
• ECMA-151 ISO/IEC 11558:1992, Specification of DCLZ (compression algorithm). [4]
• ECMA-170 ISO/IEC 12447:1993, Specification of DDS (for 60m and 90m tapes). [5]
• ECMA-171 ISO/IEC 12448:1993, Specification of DATA/DAT-DC (for 60m and 90m tapes). [6]
• ECMA-198 ISO/IEC 13923, Specification of DDS-2. [7]
• ECMA-236 ISO/IEC 15521, Specification of DDS-3. [8]
• ECMA-288 ISO/IEC 17462, Specification of DDS-4. [9]

view • talk • edit	Magnetic tape data storage formats
	Linear	Helical-Scan
Three Quarter Inch (~19 mm)	LINCtape (1962) - DECtape (1963)	Sony DIR (19xx) - Ampex DST (1992)
Half Inch (12.65 mm)	UNISERVO (1951) - IBM 7 Track (1952) - IBM 9 Track (1964) - IBM 3480 (1984) - DLT (1984) - IBM 3590 (1995) - T9840 (1998) - T9940 (2000) - LTO Ultrium (2000) - T10000 (2006)	Redwood SD-3 (1995) - DTF (19xx) - SAIT (2003)
Eight Millimeter (8 mm)	Travan (1995) - IBM 3570 MP (1997)	Exabyte (1987) - Mammoth (1994) - AIT (1996) - VXA (1999)
Quarter Inch (6.35 mm)	QIC (1972) - SLR (1986)
Four Millimeter (3.8 mm)	DC100 (1976) - DECtapeII (1979)	DDS/DAT (1989)
One Eighth Inch (3.18 mm)	KC Standard, Compact Cassette (1975) - Datassette (1977)
Stringy (1.58 - 1.9 mm)	Exatron Stringy Floppy (1979) - ZX Microdrive (1983) - Rotronics Wafadrive (1984)