DDS DAT Technology

DAT, or to give its correct name DDS DAT (DDS is the acronym for Digital Data Storage) was born in the late 1980s when Hewlett Packard and Sony decided to develop Digital Audio Tape as a data backup medium.

DAT had been born of the need in the music industry to have high quality tape recordings without the hiss and whirr associated with analogue tape.

With quite a lot of technical effort and the addition of an extra level of error correction (DAT already had C1 and C2 so unsurprisingly C3 error correction was born) a digital data storage format was born.

Initially using 60m tapes and recording 1.3GB of data the format added compression to give an estimated 2.6GB storage capacity and outperform its 8mm rival from Exabyte. It also considerably outperformed the leading QIC drive available with its comparatively low 525MB storage. The introduction of 90m tapes took the native non-compressed capacity to 2GB, 4GB with compression.

The format still has dominance in the lower end storage market, being far behind its heavy duty rivals LTO and DLT, but still offering a competitive cost of ownership for lower capacity requirements.

Since DAT72 was introduced to the market back in 2003 it has taken 4 years for 6th generation of DAT to be unveiled. June 2007 saw HP announce their DAT160 drive. To increase transfer speeds and capacity, DAT160 has now moved from the 4mm tape width of previous generations to an 8mm format. The drive however is still backwardly read compatible with DDS4 and DAT72.

DAT uses helical scan recording method similar to Exabyte and AIT (as opposed to the serpentine or linear method of recording employed by DLT and LTO technology). The recording media is 4mm wide for DDS1 - DDS4 and DAT72 and uses 8mm wide media for DAT160.

With helical scan recording, data is written to a relatively slow moving tape via a fast spinning read/write head drum. This technology has the reported benefit of greater head durability, and reduced shoe-shining effect, the to and fro-ing tape motion that can occur in linear recoding if data is not slower than the recoding speed.

The external properties of a 4mm DAT are 73mm x 54mm x 10.5mm (L x W x D) and uses a cassette type format where the source and take-up spool are housed within the cassette. The 8mm DAT160 is deeper at 14.7mm.

Further Reading: DAT Technology - (The DAT Manufacturing Group)

Data recovery from DAT cartridges has tended to be related to media wear (through overuse), casing damage by bad handling and tracking issues caused by drive wear. Considering the shear volume of DAT drives, it has performed admirably with a disproportionately low level of problems.

Early drives in 1994 to 1995 had more of a tendency towards drive wear leading to tape position problems and recording errors, but these often related to drives being overused and inadequate quality checks in the backup regimes of those using the drives.

4mm DAT cartridges are small and they do have quite a fragile door mechanism which is used as part of the load/unload mechanism. Damage to this can lead to a tape not unloading correctly, then damage to the front end of the media leading to a requirement for data recovery.

The usual human error problems relating to tape overwriting and re-initialisation come into play with DAT as much as with any other medium and, being quite light they don't stand up to extreme heat as well as some of the larger formats, though our engineers have been able to successfully recover data from fire damaged DAT tapes where the outer casing have extensively melted and only partial damage to the actual recording media.

Generation	Native Capacity	Data Rate (MB/s)	Year	Tape Length	WORM	Encryption
DDS1	20GB	0.183	1989	60m	No	No
DDS1	2GB	0.183	1990	90m	No	No
DDS2	4GB	0.72	1993	120m	No	No
DDS3	12GB	1.5	1996	120m	No	No
DDS4/DAT40	20GB	1-3	1999	150m	No	No
DAT72	36GB	3	2003	170m	No	No
DAT160	80GB	5	2007	150m	No	No
Planned Implementations
7th Gen.	~150GB	8
8th Gen.	~300GB	16