The New Ultra ATA/66 Interface: A Highly Reliable, Cost-effective Solution To PC Users' Need For Speed.

Bigger, more capable operating systems on the desktop. Bigger, more media-rich files on the hard drive. Higher capacities, faster rotational speeds, and, hence, faster internal transfer rates within the drive itself. It all could have spelled trouble for desktop users by way of turning the drive/host connection into a system performance bottleneck. PC users, then, would have faced ever-longer waits for applications to pop up on their computer screens--at a time when speedier and more reliable access to data has become less a luxury than an imperative for virtually the entire PC marketplace.

The good news is a new interface technology has emerged that eliminates this specter: Ultra ATA/66, an extension to the current Ultra ATA/33 interface standard. Ultra ATA/66 doubles ATA/IDE drives' external transfer rate to an unprecedented 66MB/sec--fast enough to stay well ahead of internal drive transfer rates into the new millennium. It leverages mature technologies not only to meet the heightened throughput demands that large, complex files place on desktop systems, but also to address PC users' equally critical requirements for enhanced data integrity and data availability. By retaining full backward compatibility with current ATA systems and drives, Ultra ATA/66 can provide all these advantages at a cost that won't break PC users' budgets (See Editor's Note, at the end of this article).

Developed by Quantum, Ultra ATA/66 has won support from Intel Corp. plus eight of the world's largest PC manufacturers: Acer, Compaq Computer Corp., Dell Computer Corp., Fujitsu, Gateway, Hewlett-Packard Co., IBM Corp., and NEC Corp. In addition, all of the leading hard drive manufacturers, including Fujitsu, IBM, Maxtor, Seagate Technology, and Western Digital, together with leading suppliers of adapter cards, BIOS, cables, chip sets, and testers have also endorsed the technology as the next-generation PC drive-level interface. Quantum is widely licensing the technology to enable industry standardization.

The result is hard drives that enable both enhanced data integrity and faster data access for PC users--along with an overall cost structure consistent with desktop computing requirements--are now being shipped by a number of drive manufacturers. What follows is a brief explanation of how Ultra ATA/66 will deliver these important benefits.

THE CONTINUING NEED FOR SPEED

The internal or media data rate of hard disk drives is increasing at approximately 40% per year. This increase is driven partly by increased linear bit density on the disk and partly by increases in rotational speed. If the industry stayed with the current Ultra ATA/33 interface, by the year 2000 the interface would become a bottleneck and the performance of the PC would be held back by the drive.

THE EFFECT OF BUFFERING

One way to visualize the data transfer rate/buffering paradigm is through a faucet, sink, and drain analogy. During a read operation, the faucet represents data coming from the disk, while the sink is the buffer and the drain is the ATA interface to system memory. When data trickles from the faucet, as is the case with random data transfers (small files, etc.), then a small sink and a narrow drain are quite adequate. But when it streams in a continual flow, as in sequential transfers, then a narrow drain necessitates a large sink to avoid a constant turning off-and-on of the faucet (i.e., slipped revs). Widening the drain appropriately, on the other hand, means you can get away without having to put in a larger sink or buffer. The idea behind Ultra ATA/66, then, is to increase the size of the "drain" in order to increase throughput by transferring data much more quickly--and, along the way, eliminating the need for more extensive buffers, effectively keeping costs down.

CRC EQUALS EXCEPTIONAL DATA INTEGRITY

On the data availability front, Ultra ATA/66 employs proven Ultra ATA/33 technology to ensure exceptional integrity of transferred data. That technology is Cyclical Redundancy Check (CRC), a powerful data protection verification method for hard drives.

With CRC, verification code is produced for each burst data transfer by both the host and the drive, and is stored in their respective CRC registers. At the end of each burst, the host sends the contents of its CRC register to the drive, which compares it against its own register's contents. This data integrity assurance is carried forward from Ultra ATA/33.

80-CONDUCTOR CABLE IS KEY TO SPEED AND DATA INTEGRITY

In addition, the Ultra ATA/66 specification replaces a 40-conductor cable with an 80-conductor cable to ward against electronic noise interference, or signal crosstalk, and so enhance data integrity even more. This cable is plug compatible with today's Ultra ATA/33 drives and headers.

The pin side of the connector on the 80-conductor cable is identical to the connector for today's 40-conductor cable. Inside the connector, the 40 additional ground lines are connected to the existing ground pins in the 40-pin connector. This ensures complete plug compatibility with existing drives and systems. In fact, there are some Ultra ATA/33 systems shipping today that use the 80-conductor cable to reject noise from power supplies or floppy drives.

Use of an 80-conductor cable also has enabled Quantum to double the Ultra ATA burst data transfer rate--simply by streamlining data management within the drive. Specifically, the new cable specification makes it possible to halve setup times prior to signal read operations, which occur at the beginning of each burst data transfer.

Before the drive controller reads a signal, it must "look" at the data lines to determine whether they have switched to a high or low state (i.e., a one or a zero). If the controller examines the lines too soon after the previous data burst, they might still be somewhere between high and low. Hence, the controller must wait for the lines to "settle down" to ascertain the current state. This waiting period is referred to as the setup time.

The addition of 40 extra ground lines to the Ultra ATA cable spec considerably reduces signal crosstalk and ringing between the data lines. This allows the lines to "settle down" much faster, thereby slashing setup times in half. And this is what enables the Ultra ATA/66 interface to transfer data at twice the Ultra ATA/33 rate without requiring any other significant changes to the Ultra ATA specification, especially to the DMA protocol.

The 80-conductor cable is mandatory for running Ultra ATA/66. The usual 40-conductor ATA cable cannot handle the higher speed and, because the cables are plug compatible, the system must determine the presence of the correct cable.

This detection is achieved by having a break in one of the lines on the 80-conductor cable that is normally an unbroken connection in the existing cable. If this break is detected, the system BIOS on Ultra ATA/66 compatible systems can instruct the drive to run at the correct speed for the cable type detected.

SO WHAT IS NEEDED TO RUN AT 66MB/SEC?

* A drive that is capable of Ultra ATA/66.

* A system that is capable of running Ultra ATA/66 from the chipset or via an Ultra ATA/66 adapter card.

* An 80-conductor (40-pin) ATA cable.

BACKWARD COMPATIBILITY REINS IN COSTS

Retaining the DMA protocol, in turn, is one of the features that makes Ultra ATA/66 a fully backward compatible and, hence, low-cost solution to the PC users' need for speedy data access. The interface's compatibility with many earlier Ultra ATA/33 motherboards and controllers means Ultra ATA/66 should be simple for PC manufacturers, distributors, and their customers to implement. It also will enable PC vendors and distributors to streamline their inventory management. This all adds up to considerable cost savings that, in turn, can be passed on to PC users.

Such backward compatibility also means IT organizations won't have to incur the substantial costs of switching to an alternative, expensive, high-speed interface technology and replacing their entire PC storage infrastructures to enable faster data access for functions or departments that need it. Instead, they can purchase Ultra ATA/66 drives and use them both in newer ATA systems that take advantage of the higher-speed interface and in older Ultra ATA/33 systems where they will automatically fall back to Ultra ATA/33 speeds. (See Editor's note) In addition, distributors, VARs, and manufacturers will not get stuck with inventory of incompatible interface drives and the transition can be easily managed.

Alternative interfaces certainly will play a role in the PC universe, especially for specialized environments such as consumer electronics peripherals. But for the general run of desktop computing applications, Ultra ATA/66 will provide PC users with a low cost, fast access, highly reliable interface solution for years to come.

Steve Wilkins is the program director of strategic and technical marketing at Quantum Corp. (Milpitas, CA).

EDITOR'S NOTE: Ultra ATA/66 drives have been shipping for a few months. During testing of early drives, a problem with certain motherboards was noted. The problem, identified by IBM, relates to some motherboards with VIA chipsets and the award BIOS. In order to use Ultra ATA/66 drives on these motherboards, a separate Ultra ATA/66 controller must be used or the drive must be set to run as an Ultra ATA/33 drive.

It should be clear, too, that Ultra ATA/66 drives used on systems that only support Ultra ATA/33 will only run at Ultra ATA/33 speeds. The true performance benefit can only be achieved using a motherboard or controller card that fully supports Ultra ATA/66.

Ultra ATA/66 adapters may offer additional features that motherboards with Ultra ATA/66 don't provide. For example, an Ultra ATA/66 adapter board from Promise Technology and possibly other vendors offer RAID capabilities. A RAID array, made using the less expensive Ultra ATA/66 hard drives, may be a compelling alternative to low- end SCSI RAID arrays.