A USB system has an asymmetric design, consisting of a host controller and multiple devices connected in the form of trees by using special hub devices.
USB design is intended to eliminate the need for adding expansion card to computer ISA or PCI bus, and improve the ability of the plug-and-play (plug-and-play) by allowing devices to be exchanged or added to the system without needing to reboot the computer. When the USB is installed, he was immediately recognized and processing computer system device drivers needed to run it.
USB can connect additional equipment such as computer mouse, keyboard, scanner images, digital cameras, printers, hard disk, and networking components. USB is now the standard for multimedia devices such as scanners and digital camera images.
The latest version (up to January 2005) USB is version 2.0. The most striking difference between old and new version is a much improved transfer speeds. USB data transfer speed is divided into three, among others:
* High speed data with clock frequency 480.00Mb / s and a tolerance of ± 500ppm signaling data.
* Full-speed data with clock frequency 12.000Mb / s data signaling and tolerance at ± 0.25% or 2.500 ppm.
* Low-speed data with clock frequency 1.50Mb / s data signaling and tolerance at ± 1.5% or 15.000 ppm.
Source :http://id.wikipedia.org/wiki/Universal_Serial_Bus
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