USB 2.0 Storage Zooms Ahead

Electronic News, Jan 15, 2001 by Jack Wood, Orrin Tallman

VERSION 2.0 OF THE USB interface promises to increase the usability and performance of consumer electronics. With a data transfer rate of 480Mbit/sec., USB 2.0 certainly trumps the earlier l2Mbit/sec. USB 1.1 and is faster than the IEEE 1394 standard's 400Mbit/sec. maximum throughput. USB 2.0 promises to live up to its "universal" appellation by becoming the preferred way of connecting popular peripherals such as computer mice, scanners, storage devices and digital cameras, to PCs and even Internet appliances (LAs).

One of the many exciting areas for USB 2.0 is its application in the mass storage market. While plug-and-play enabled, speeds on USB 1.1 CD-R and CD-RW drives were limited by the standard's limitations. But with the first ATA/ATAPI-to-USB bridge chips now passing the compliance testing standards of the USB Implementers Forum (USB-IF), storage peripheral manufacturers will be able to quickly introduce high-speed, USB 2.0 CD-R, CD-RW, DVD-RAM and magneto-optical drives, among others.

With USB's bandwidth increasing to its present range, the USB standard is fast becoming a very desirable interface for the high-bandwidth peripherals that have historically relied on non-plug-and-play interfaces such as SCSI and ATAPI. While USB 1.1 has been used for CD-RW drives from such manufacturers as QPS and Sony, the write speed has been limited to 4X. Still, many consumers gladly traded off the higher performance of an internal ATAPI CD-RW or external SCSI drive for the superior convenience and ease of use of a USB-equipped CD-RW drive. With the advent of the much faster USB 2.0 specification, consumers will no longer have to trade off performance for ease of use. Enthusiasts can now buy USB 2.0 CD-RW drives with write speeds of up to 16X.

Instead, the question will become one of which high-speed interface to use. An obvious question is: How does USB 2.0 compare to IEEE 1394 (called Fire Wire by Apple Computer and i.Link by Sony Corp.)? A simple benchmark, consisting of copying 253Mbytes' worth of MP3 files, answers the question nicely. The testing was performed using two Maxtor drives and a 450MHz Pentium II Dell Dimension running Windows 2000. One Maxtor drive was connected to a IEEE 1394 host controller using the Maxtor brand IEEE 1394 bridge; the other drive was connected to the Dell Dimension via a USB 2.0 host controller using the ISD-300 bridge chip. The USB 2.0-connected drive wrote data at a rate of 10.2Mbyte/sec. compared to 8.7Mbyte/sec. for the IEEE 1394-connected drive.

As a comparison, the MP3 files copied to a second internal hard drive configured as a slave device on the same IDE bus resulted in a data rate of 4.8Mbyte/sec. The internal drives were an UltraATA/66 Quantum Fireball LCT10-10 operating at 5,400RPM and an UltraATA/66 IBM DPTA-371360 operating at 7,200RPM.

In this particular benchmark, the USB 2.0 drive had the fastest transfer rate, followed by the IEEE 1394 drive, then the secondary ATA hard drive. Why was copying to a USB 2.0 drive so much faster than copying to a second internal hard drive? The two internal drives had to share the same IDE bus, which can only address one of the drives at a time. Moving the second drive to the USB 2.0 bus allowed for simultaneous access by both the internal IDE drive and the external USB 2.0 drive.

Jack Wood is the USB 2.0 program manager and Orrin Tallman is the ASIC project manager for In-System Design Inc., Boise, Idaho.