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Bandwidth and Speed

USB supports three different speeds:

Low-speed devices operate at 1.5 Mb/s - Typical examples include keyboards and mice.

Full-speed devices operate at 12 Mb/s - Typical examples include web-cams and printers.

High-speed devices operate at 480 Mb/s - Typical devices include external CD-ROM and DVD drives.

Low-speed and full-speed devices are collectively known as "classic" devices. All USB Host Controllers and Hubs support any mixture of classic devices. All USB 2.0 Host Controllers and Hubs support hi-speed devices, in addition to classic devices.

Power

USB devices are classified according to their power consumption requirements:

Low-power devices may consume up to 100mA from the USB. Typical examples include joysticks and mice.

High-power devices may consume up to 500mA from the USB. Typical examples include webcams and certain keyboards with embedded hubs.

Self-powered devices may consume up to 100mA from the USB. Any additional power requirement must be drawn from an external (to USB) supply. Typical examples include printers and scanners. For most practical purposes self-powered devices can be considered identical to low-power devices.

It must be recognised that USB has no capability to measure the power that is actually consumed. Although the PC operating system may disallow certain device configurations due to the power budget being exceeded, the decision is based on the software description of device power requirements, not on actual measured values.

ExtremeUSB Technology

ExtremeUSB technology, invented by Icron Technologies Corporation, enables USB peripherals to be placed wherever users need them, up to 2 km (1.2 miles) away from a host computer. With ExtremeUSB technology, peripheral devices function as if they are within the 5 meter (16.4 foot) limit specified by USB-IF.

Icron's communications protocol preserves standard USB functionality and timing restrictions while accommodating the increased cable delay incurred in extended range transmissions.

This technology can be incorporated into products by Original Equipment Manufacturers (OEMs), or purchased as a stand-alone product through one of Icron's distribution partners.

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