Basically the main difference between USB 2.0 and 3.0 is the improved performance of the latter. With this reason, USB 3.0 is no doubt more expensive than USB 2.0. USB 2.0 was first released in April 2000 and has a speed of 480 Mbps which is why it is classified as a High Speed (HS) device. It utilizes a polling mechanism where it can either receive or send data (Half Duplex). It consumes about 500 mA and contains 4 wires in its cable. It is available in Standard-A connector which is grey in color, and in Standard-B which is smaller in size. It can reach up to 5 meters in length.
8 years later, USB 3.0 is released and works 10 times faster than USB 2.0 with a speed of 4.8 Gbps. With this, its is classified as Super Speed (SS) device. It utilizes an asynchronous mechanism in which it can receive and send data simultaneously (Full Duplex). It consumes 900 mA and permits power efficiency as it consumes less power in idle states. It has 9 wires in each cable. Standard-A connector is blue in color while Standard-B has extra space for wires. Lastly it can reach up to 3 meters in length which is shorter than that of USB 2.0.