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USB 2.0 Intefaces

While USB was originally designed to replace legacy serial and parallel connections, notwithstanding the claims that they were complementary technologies, there can be little doubt that USB 2.0 specification was designed to compete with FireWire. Compaq, Hewlett-Packard, Intel, Lucent, Microsoft, NEC and Philips jointly led the development, with the aim of dramatically extending performance to the levels necessary to provide support for future classes of high performance peripherals.

At the time of the February 1999 Intel Developer Forum (IDF) the projected performance hike was of the order of 10 to 20 times over existing USB 1.1 capabilities. However, by the end of the year the results of engineering studies and test silicon indicated that that was overly conservative, and by the time the USB 2.0 was released in the spring of 2000, its specified performance was a staggering 40 times that of its predecessor.

USB 2.0 in fact defines three level of performance, with Hi-Speed USB referring to just the 480 Mbit/s portion of the specification and the term USB being used to refer to the 12 Mbit/s and 1.5 Mbit/s speeds. At 480 Mbit/s, any danger that USB would be marginalised by the rival IEEE 1394 bus appear to have been banished forever. Indeed, proponents of USB continue to maintain that the two standards address differing requirements, the aim of USB 2.0 being to provide support for the full range of PC peripherals – current and future – while IEEE 1394 specifically targets connection to audio visual consumer electronic devices such as digital camcorders, digital VCRs, DVD players and digital televisions.

While USB 1.1’s data rate of 12 Mbit/s, was sufficient for many PC peripherals, especially input devices, the higher bandwidth of USB 2.0 is a major boost for external peripherals as CD/DVD burners, scanners and hard drives as well as higher functionality peripherals of the future, such as high resolution video conferencing cameras. As well as broadening the range of peripherals that may be attached to a PC, USB 2.0’s increased bandwidth will also effectively increase number of devices that can be handled concurrently, up to its architectural limit.

USB 2.0 is fully backwards compatible – something that could prove a key benefit in the battle with IEEE 1394 to be the consumer interface of the future, given its already wide installed base. Existing USB peripherals will operate with no change in a USB 2.0 system. Devices, such as mice, keyboards and game pads, will not require the additional performance that USB 2.0 offers and will operate as USB 1.1 devices. Conversely, a Hi-Speed USB 2.0 peripheral plugged into a USB 1.1 system will perform at the USB 1.1 speeds.

While Windows XP did not support USB 2.0 at the time of its release in 2001 – Microsoft citing the fact that there were no production quality compatible host controllers or USB 2.0 devices available in time as the reason for this – support had been made available to OEMs and system builders by early the following year and more widely via Windows Update and the Windows XP SP1 later in 2002.

Since the USB 2.0 Specification encompasses all USB data transfer speeds – low (1.5MMbit/s), full (12Mbit/s) and high (480Mbit/s) – the USB Implementors Forum (USB-IF) sought to avoid confusion in the marketplace by introducing the terminology Hi-Speed USB to refer to the 480Mbit/s portion of the specification. However, despite the USB-IF’s best efforts to ensure that vendors used the certified USB Logos appropriately, manufacturers were slow to switch to the new naming conventions and were often inconsistent in their use of it.

Filed Under: Interfaces

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