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DAT Technology

Within the tape market there is a wide range of tape technologies; the question for SMB customers is which one to choose. The answer is clear - DDS/DAT, a technology that continues to flourish because it meets the needs of the SMB market for cost-effective, reliable backup better than any other technology available.

DAT was first introduced in 1989 and today it continues to be the unit volume leader in the low-end tape drive market for smaller businesses. Since then, we have seen the DDS/DAT format go through six generations of product, from DDS-1 to DDS-4, DAT 72, DAT 160 and more recently DAT 320. This has created a massive world-wide installed base of over 6 million drives in current operation, and a grand-total of over 18 million DAT drives shipped since its introduction in 1989. With the seventh generation DAT 320 format recently available, the technology continues to keep pace with the performance and capacity needs of smaller business environments.

Unlike AIT, VXA, ADR, SLR, DLT and SDLT, DDS/DAT is based on an open standard format for data interchange. The influential DAT manufacturers group presides over this open standard with verification processes that ensure compliance. With multiple manufacturers developing and shipping DDS/DAT products, customers benefit from increased competition, which leads to better prices, faster development and more choice.

The DAT Manufacturers Group is continuing to invest in DAT technology; the published roadmap shows the development of a further generation. Not only does an investment in DAT technology provide the security of a format with a history of outstanding reliability, the legacy of backward compatibility also provides the potential for future expansion without compromising your investment in the technology.
How DAT Works

DDS format for DAT is a helical scan format where data is written diagonally across the width of the tape. The advantage is that, by allowing subsequent tracks to have different writing angles and to overlap, a much greater capacity can be achieved for a given length of tape because no guard bands are necessary. To achieve this, the rotating drum is tilted at an angle from the vertical.

Tape Azimuth Recording Pattern
The drum has four heads (two write heads and two read heads), located at 90° intervals. For each rotation of the drum, two tracks are written. The read heads verify the data that has been written (recorded) and the drive rewrites if necessary.

Transfer rate on DAT technology is determined partly by the wrap angle (amount of tape wrapped around the rotating helical scan drum) and the speed of rotation of the drum. All generations of DAT drive up to and including DAT72 featured a 90 degree wrap angle, so that the tape was in contact with a quarter of the drum. However the wrap angle of the DAT160 and DAT320 drive is 180 degrees to make more efficient use of the time tape is in contact with the head to increase transfer rate.

On DAT72 drives, write head A is in contact with the drum for 90 degrees, followed by read head A to verify the data is written correctly. The same process is repeated for write head B and read head B. While this is a secure and reliable process it leaves an “idle” time where data is not being written, and in turn this limits the transfer rate. With DAT160 and DAT320 drives, the writing and read verification is taking place for a full 360-degree revolution of the drum, making the whole write and verify process more efficient because there is no idle time.

Regardless of this difference in operation between DAT72 and DAT160/320, the open standard format continues to ensure backward compatibility between DAT320 and DAT160, and DAT160 and DAT72 in addition to full interchangeability between different manufacturers drives.
"The DDS/DAT value proposition has always been based on the pivotal points of open standards and low cost of ownership."