1.The USB 2.0 specification requires cable delay to be less than 5.2 ns per meter (192000 km/s, which is close to the maximum achievable speed for standard copper cable).
2.USB 2.0 maximum cable length is 5 metres (16 ft).
3.Although a single cable is limited to 5 metres, the USB 2.0 specification permits up to five USB hubs in a long chain of cables and hubs. This allows for a maximum distance of 30 metres (98 ft) between host and device, using six cables 5 metres (16 ft) long and five hubs. In actual use, since some USB devices have built-in cables for connecting to the hub, the maximum achievable distance is 25 metres (82 ft) + the length of the device's cable.
4. A unit load is defined as 100 mA in USB 2.0,and a maximum of 5 unit loads (500mA) can be drawn from a port in USB 2.0.