USB 2.0 and USB 3.0 differ in terms of transfer speed, power management capability and structure. USB 3.0 offers increased transfer rates, maximum bus power and better power management.
The biggest difference between USB 2.0 and 3.0 is the speed at which each can communicate with the computer's host controller. USB 2.0 offers a transfer rate of 480 Mbps. USB 3.0 offers a transfer rate of 4.8 Gbps, which is 10 times faster than 2.0, thus revolutionizing data transfer between devices and the computer. In some cases, this transfer speed depends on the device in use as well as the bus, port and cable type.
In terms of structure, the USB 2.0 connector has four wires, while USB 3.0 has an extra physical bus that doubles the wires to eight. While a USB 3.0 connector is backward compatible with a USB 2.0 port, the connection only works at 2.0 speeds.
In power usage and requirements, USB 2.0 provides up to 500mA, while USB 3.0 provides up to 900mA and facilitates bus-powering of power-hungry devices. 3.0 USB devices provide more power to gadgets and conserve power when the device is idle and during charging. The devices disconnect from power completely when not in use.