USB 2.0: A Storage Bus Whose Time Has Come - Technology Information

Computer Technology Review, Oct, 1999 by Bob Salem

The popularity of the Universal Serial Bus (USB) and changing market dynamics have made the USB a strong candidate as an interface for storage applications.

Some in the industry might think that the above statement borders on heresy. However, many of these same people predicted the demise of ATA hard disk drives (HDDs) with the arrival of IEEE 1394 (Firewire).

Today, that vision of doom and gloom has proven to be shortsighted. For several reasons, ATA-based HDDs have actually grown in popularity. The low cost of ATA drives (providing the ability to sell a PC for under $1000), faster ATA standards, and emerging embedded storage applications have breathed new life into the ATA market.

For these same reasons, the concept of the USB as a viable interface needs to be revisited. Easy to install, low in cost, and with a new higher performance standard, USB is ideal for a certain segment of the storage market.

An Overview Of The USB

USB was developed differently than other standards. The ATA/ATAPI, SCSI, and Firewire standards were first developed; then the ability to hot-plug-and-play was added. In contrast, the USB specification anticipated and incorporated hot-plug-and-play from the beginning.

The USB was designed as an interface that would make the installation of peripheral devices (up to 127) to a PC very easy. Initially, acceptance of the USB was delayed by the lack of full operating-system support on some platforms. However in the last year, with most platforms now supporting USB, it has experienced a remarkable turn-around in popularity and viability.

Today, the consumer can install a new USB peripheral on a PC and expect it to work immediately. This is a remarkable accomplishment for a new standard and an exception for the PC industry. However, as more and more users plug all types of devices into their PC's USB, the demand is growing for more bandwidth than the l2Mbit/sec offered by USB Specification 1.1.

A Preview Of The USB 2.0 Standard

There is a legitimate concern about using USB 1.1 for storage applications because its l2Mbit/sec bandwidth limitation may prevent a device from immediately accessing the bus. The market has been quick to respond to this concern, however, as well as the need for more bandwidth to accommodate applications such as video cameras.

The USB Implementers Forum has proposed a new standard called the USB 2.0, which calls for the available bandwidth to be increased to 45OMbit/sec. (Test results have shown that a future version capable of 700Mbit/sec is possible.) At the same time, the new specification allows the USB 2.0 to be backward compatible with the USB 1.1.

The USB 2.0 Vs. Other Storage Interconnect Standards

The new USB 2.0 specification allows a USB to support data transmission on a par with the ATA/ATAPI, SCSI, and Firewire interface standards. In fact, with a maximum transfer rate of 450Mbit/sec (equivalent to 56MB/sec), the USB 2.0 has more than enough speed to function well as a storage interface bus.

Incidentally, the most popular IDE/ATA drives today are the Ultra ATA 33 drives, which have a maximum transfer rate of 33MB/sec, despite the availability of higher performance Ultra ATA 66 drives. For most PC users, the difference in maximum transfer rates is insignificant in actual experience.

Not only does the USB 2.0 match most transfer rates of other interfaces, it also offers benefits that ATA/ATAPI, SCSI, and Firewire cannot provide. These benefits include:

* Ease of installation

* Hot plug and play

* Cross platform compatibility

* Portability

Ease Of Installation

Adding peripherals (such as a Zip drive, a CD-ROM drive, or other storage) to a computer has always been a problem, even for the knowledgeable user. With ATA/ATAPI, SCSI, and Firewire, the user has to choose the right interrupt level and PCI cable, configure the setup, and overcome any conflicts with other peripheral devices already attached to the computer.

Because USB 2.0 is designed to be hot-plug-and-play, installing a storage device is usually as simple as plugging the standard USB cable connector into the computer. The computer's operating system automatically handles all the interrupts, cable, formatting, and conflicts without user intervention.

Cross-Platform Compatibility

Unlike other interfaces, the USE 2.0 provides users with the ability to move peripherals from one platform to another with confidence. No matter what the platform is, USB devices will be compatible.

The USB And The Increasing Market For Portable Storage

Information in electronic format is expanding exponentially. As users become more dependent on the Internet, the need to download and store information is quickly increasing.

At the same time, society and the workplace are becoming more mobile. Today, more and more people are using notebooks--many as their only PC. These users are limited to storing data onto their notebook HDD or onto multiple floppy, Zip, or CD-R discs. None of these options are good because of cost, size limitations, and the performance penalty when running a program.