DAT group adds PRML specs

Electronic News, March 28, 1994

CUPERTNO, CALIF.--The Digital Data Storage (DDS) Manufacturers Group last week said it has added new specifications to its DDS-3 format which will boost digital audio tape (DAT) capacity to 12GB.

Hewlett-Packard said it would introduce a DDS-3 DAT drive in the second half of 1995 in a 3.5-in. form-factor.

The DAT drive will incorporate partial-response, maximum-likelihood (PRML) read-channel ICs as wel as other techniques to increase the bit density on tape. Neville Pawsey, HP's computer peripherals marketing manager, Bristol, England, said HP will design its own PRML device.

PRML read-channel technoogy is already finding its way into hard disk drives; Quantum and Texas Instruments, for example, have collaborated on the technology (EN, Feb. 14). However, the needs for tape drives would be different, so DAT makers will have to develop their own PRML ICs or partner with semiconductor companies.

Mr. Pawsey did not indicate whether HP would make its PRML technology available to other DAT makers; the company already licenses its data compression technology to several other companies. In the past, some DAT makers also have been sourcing key parts from Sony, which along with HP formed the DDS group. PRML schemes compare a detector's output with possible inputs for improved data recovery and overcome signal imperfections.

The current DDS-2 format features 4GB capacity; the original DDS-3 spefications called for 8GB capacity. One factor in the DDS group's upgrade is that makers of quarter-inch minicartridges are also attempting to boost capacity.

3M, for example, has licensed its 13GB QIC cartridge technology to Tandberg Data Storage. Tanberg is developing 5.25-in. QIC drives for IBM scheduled for availability in 1994.

The DDS-3 format, which supports 24GB capacity with data compression, will be specified with a transfer rate ranging from 720KB/sec. to 1.5 MB/sec. While QIC makers are pushing data transfer rates as well (Tandberg's 13GB QIC drives are targeted to function at 1.5MB/sec.), Mr. Pawsey claimed that DAT drives are not really at a disadvantage. He said that in the case of data stream failures while information is being transferred to the back-up tape drives, DAT mechanisms are able to restart faster than QIC devices. "On paper there are transfer rate advantages (for QIC)," he said.

Meanwhile, QIC drive suppliers are also moving to new technology in order to increase capacity, such as embedded servos and thin-film magneto-resistive (MR) read elements (EN, Aug. 16, 1993). 3M has a pact with Applied Magnetics to jointly develop MR head technology; on the media side, there may be a move to barrium ferrite, now used in Florptical storage devices.

Mr. Pawsey, though, contends that DAT drives will essentially use the same design as they move to higher capacities. Mr. Pawsey noted that the bit density in the DDS-3 format will be achieved without changes to the read head design. Still, the DDS-3 specification calls for two flux transitions under heads at a given time compared to one flux transition with the DDS-2 standard.

Mr. Pawsey said PRML techniques will result in fewer ASICs but that overall the helical-scaqn based DAT mechanisms will be similar. Drum speeds may even be slower, he added.

As a result of the design's stability, Mr. Pawsey said he believed that DAT makers will be able to move faster on their migration path. The DDS group plans a new specification for 24GB native capacity; first products using new metal-evaporated media and 180-meter tape are planned to be available in 1977. The DDS-3 specification is based on 125-meter media.

HP, however, is also a player in the QIC arena through its acquisition of Colorado Memory Systems. Mr. Pawsey said the company remains committed to DC2000 QIC technology for the PC back-up market. The DDS-3 based DAT drive, meanwhile, will be positioned to take an 8 mm and DC6000 tape technology for PC LAN servers and Unix workstations. The DAT drive will feature a SCSI-2 interface.

HP's DDS-2 DAT drive was introdeced with a 510KB/sec. transfer rate while other companies followed with products at 366KB/sec. Mr. Pawsey, though, would not elaborate on HP's plans for the DDS-3 generation.

Robert Hill, marketing manager for HP's Bristol Division, said: "This development ensures that DDS will keep pace with trends in network and workstation data back-up, archival and interchange. DDS will continue to be the technology of choice for cost-effective, medium- to large-scale removable data-storage applications, but not it can vie for a variety of image-processing and multimedia applications as well."

According to International Data Corp., HP holds 42.2 percent of the 4mm DAT market, followed by Conner Peripherals with 34.8 percent, Rexon at 16.5 percent, Sony at 5.3 percent and Exabyte at 1.3 percent. Conner's stake was acquired through its acquisition of Archive; Exabyte, meanwhile, bought R-Byte, Inc., to gain DAT technology.