From DDS-1 to DAT 72: a brief history of DDS media - Tape/Disk/Optical Storage

Computer Technology Review, July, 2003 by Dan Murphy

The arrival of DAT 72 technology has given a mid-life boost to the 4mm Digital Data Storage (DDS) format with an affordable tape drive solution that offers a convenient, backward- compatible upgrade path to high-capacity backup for the huge installed base of DDS users. This fifth-generation implementation of the DDS format takes the technology to 72 Gigabytes (GB) per cartridge assuming 2:1 data compression, an 18x improvement over first-generation 2GB products. The manufacturers supporting the DAT 72 introduction are Hewlett Packard and Seagate on the hardware side, and Maxell is the premier media supplier.

The emergence of DAT 72 is good news for a technology segment that is often overlooked with much of the industry attention focused on the high-end battle between SuperDLT and LTO. However, DDS technology is the most popular tape drive technology ever--with an installed base of nearly 7 million drives--and still dominates the low end of the tape drive market with a 58% market share in 2002, according to Freeman Reports.

At the heart of DDS technology is the compact 4mm data cartridge, such as that supplied by Maxell Corporation, who for the last 30 years has been dedicated to being first to market with next generation product. The media improvements over five product generations form the basis of the continued capacity improvements for DDS. The evolution of DDS media is closely linked to the continuous improvements in metal particle coating technology. In fact, metal particle media dominates digital data storage media today thanks to the inroads made with the first generations of 4mm DDS and 8mm helical scan data recorders when most computer tape products were based on standard ferric oxide media.

DDS media introduced metal particle as a viable technology for high-density digital data storage and, today, MP media dominates the digital data storage market. DLT, Super DLT, LTO, IBM Magstar and other popular media formats, in addition to 4mm DDS, rely on MP formulations for reliable, high-density data recording.

The move to MP media from the gamma ferric oxide and chrome tape formulations that were widely used at the time was necessitated by the higher recording densities demanded by the 4mm format to compensate for the small form factor of the cartridge. The compact 4mm DDS cassette was a true breakthrough that allowed multi-gigabyte capacities in a 3.5-inch form factor. The downside of this small size was the limited amount of tape inside the cartridge. The DDS-1 format utilized 90-meter length, meaning that there were less than 50 square feet of available tape on which to record data. The quarter-inch cartridge tapes at the time offered only one-fourth of the capacity as a DDS-1 tape, but packed more than five times the physical recording area inside the cartridge.

The physical properties of MP media were quite attractive to meet the demands of DDS helical scan recording. Metal particle media offered twice the coercivity and twice the remnant flux density of alternative media pigments, producing the potential for significantly higher recording densities compared to quarter-inch or half-inch cartridge formats.

Although MP media provided much higher magnetic output, there was also a major issue with technology. MP formulations use a pure metal particle, making the media particles more environmentally sensitive and susceptible to oxidation. When MP media oxidizes, it destroys not just the recording layer of the tape, but any data that was stored on it as well.

To prevent oxidation problems and still take advantage of the high recording density potential of MP media, metal particles used in DDS media are typically coated with a passivation layer material. Maxell's Ceramic Armor coating is an example of a passivation layer that protects the metal particles against oxidation and corrosion while maintaining high signal output. This coating technology provides a thin Ceramic Armor protective layer around a pure iron core that effectively localizes the particles' energy and maintains their stability over the long term. In addition to oxidation prevention, coating metal particles with a protective layer offers two other major advantages: excellent heat resistance and increased durability. Extreme heat conditions can build up inside a DDS drive, leading to deterioration of the magnetic properties of metal particles. The thin Ceramic Armor securely protects metal particles from the effects of extreme heat, preserving the particles' magnetic properties and signal output. Similarly, the protective coating layer preserves metal particles from damage that high-speed head scanning can cause and makes a significant contribution toward improving durability.

In addition to conquering oxidation problems, another issue faced by the DDS industry was how to prevent lower-grade audio DAT media from being used inadvertently to store critical data files. Audio-grade DAT media cassettes are physically compatible with DDS-qualified media, yet cost much less. To preclude customers from being tempted to save money by using inferior grade media for data grade applications, the Media Recognition System was developed. MRS-enabled media embeds a section of stripes on the tape leader that the drive recognizes as media certified for digital data storage. DDS-MRS drives that detect MRS media will enable data-write operations. DDS tapes without MRS stripes become read-only.