4MM DDS Tape

Digital Data Storage (DDS) is a format for storing computer data on a Digital Audio Tape (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 scanning 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, AIT, VXA, and Travan formats.

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-2

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

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 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. 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 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.