Digital Data Storage
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| 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 |
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 4 millimeter (more accurately: 3.8 mm) wide tape. Initially, the tape was 60 or 90 meter long, although advancements in materials technology has 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. Image:DSS1 Tape wScale.JPG
Contents |
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.
DDS-2
Stores up to 4 GB uncompressed (8 GB compressed) on a 120 meter cartridge.
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.
DDS-4
DDS-4 stores up to 20 GB uncompressed (40 GB compressed) on a 150 meter cartridge.
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.
DAT 160 was expected in 2005.
