There are a large number of tape formats and it is hard to keep track of them all, especially with their different generations. This Techworld article is one of a series that will describe many of them and enable you to better compare an AIT tape drive, say, against an LTO or SDLT one. We start at the entry level with details of the QIC and DAT/DDS tape formats and include some road map details.

QIC
Old entry level. This is a long-lived ¼ inch catridge (QIC) tape format with serpentine recording. There is one head, which reads or writes a track at a time. Tracks are parallel to the tape. If a file is on track 3 then the head must read all of track 1 and track 2 before starting track 3. It is not the fastest of formats. Traditional suppliers were HP and Seagate and Imation, for example, supplied media. A current drive supplier is Seagate's tape division, now called Certance, with its TapeStor brand. Some examples of the format are:

Travan-20 HP Colorado Travan40
Raw Capacity 10GB 14GB 20GB
Compressed Capacity 20GB 28GB 40GB
Raw Transfer Rate c60MB/min 1MB/sec
Compressed Transfer Rate c120MB/min 2MB/sec
Notes IDE, SCSI-2 and USB IDE IDE. Overland's VR2 technology.

DAT/DDS
Veteran entry level tapes for the embedded PC/server tape drive market. This is a 4mm helical scan technology based on digital audio tape (DAT), named digital data storage (DDS) and supplied by Sony, Seagate and HP. Sony owned most of the intellectual property with HP owning the rest. After the fourth generation Sony withdrew and promoted its own Advanced Intelligent Tape (AIT) format instead. Seagate and HP devised a follow-on fifth generation, called DAT-72, and there is a roadmap for the future. DAT-72 is backwards read-compatible with DDS-3 and DDS-4 cartridges, which helps users of those formats upgrade to DAT-72.

The DDS market is the largest installed tape customer base in terms of drives; DDS represents approximately half the total tape units shipped worldwide, according to the Gartner 2002 Tape Drives Market Report, published in 2002.

According to some suppliers, the DDS market is in decline and several formats are positioned as replacements, for example, Sony’s AIT-1 and Quantum’s VS 80. Exabyte’s VXA is also aimed at this part of the tape market. HP and Seagate’s tape division, now called Certance, don’t agree.

DDS-2 DDS-3 DDS-4 DAT-72
Raw Capacity 4GB 12GB 20GB 36GB
Compressed Capacity 8GB 24GB 40GB 72GB
Raw Transfer Rate c720KB/sec 1.5MB/sec 3MB/sec 3MB/sec
Compressed Transfer Rate c1.4MB/sec 3MB/sec 6MB/sec 6MB/sec
Available from 1993 1996 1999 2003
Notes 120m tape 125m tape. Better error resistance 150m tape. Reads and writes DDS-2 and 3. 170m tape. Thinner tracks. Sealed chamber. reads and writes DDS-4 and 3.

More information about the DAT standard and its future roadmap can be found on the DAT website at www.DATMGM.com.

The DDS roadmap has a further two generations outlined. These may be called DAT-140 and DAT-240. Potential capacities, transfer rates and availability are:

'DDS-6' 'DDS-7'
Raw Capacity 70-80GB 120-160GB
Compressed Capacity 140-160GB 240-320GB
Raw Transfer Rate 5MB/sec 8MB/sec
Compressed Transfer Rate 10MB/sec 16MB/sec
Available 2005 2007

Future documents will describe ADR, SLR, DLT, SDLT, AIT, S-AIT, VXA, LTO and IBM and StorageTek formats.