USB is the answer to the development of all the new external peripherals for the PC platform. USB is low cost, fast, easy to use, bi-directional, and capable of real time data transfer of voice, audio, and video. Currently, USB 2.0 has a bandwidth of 480 Mbps, which is 40 times greater than the previous version - USB 1.1 - with a fully compatible bandwidth of 12 Mbps. You might ask why only 127 different devices can be connected to a USB system. The reason is that a USB system uses addresses to identify different devices. The address field in a USB packet is seven bits long. The number of addresses you can create with this is two to the power of seven - 128 unique addresses. Address 0000000 is reserved for the default address and it is assigned to all devices upon power-up of the system. That leaves addresses 0000001 to 1111111 to use for the USB devices.
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