USB Universal Serial Bus
The USB standard provides a fast Master/Slave interface in star topology with max 127 devices. Each cable section is 5 metres (with up to 6 hubs, a max distance of 30m). Low-Speed 1.5 Mbit/s and Full-Speed 12 Mbit/s, 5V 500mA of power (limited to 100mA during startup).
The 2.0 specification is the addition of a High-Speed 480 Mbit/s data transfer mode. USB 3.0 it is backward compatible with USB 2.0, supplying more power (900mA) and it also adds a Super-Speed >4.8 Gbit/s data transfer mode.
A short range high speed radio communications protocol (480 Mbit/s up to 3 m and 110 Mbit/s up to 10 m).
The USB 2.0 specification defines a host computer with reduced abilities, which can be used in devices that only connected to the a single USB peripheral.
USB 1.0 and USB 2.0 use a cable with 4 wire (Vbus, Gnd, D+ and D-), USB 3.0 need 8 wire (Vbus, Gnd, D+ and D-, SSrx- + SSrx+, SStx- + SStx+). For recognize a devise and speed the devise put 3V (1,5KOhm pul up resistor) to D- wire (low-speed) or to the D+ wire (full-speed/high-speed need more informations/Handshake on the D+ wire).