USB 3.0 requires that each pair in the cable assembly be shielded to withstand the electromagnetic interference (EMI) inherent with transmissions at higher frequencies.
Although all connectors are compatible with all receptacles, to attain SuperSpeed performance, SuperSpeed connectors with five additional pins must be used on cables and receptacles. These pins do not obstruct the four legacy pins required for backward compatibility. Instead, they sit farther back and are accessible only to compatible interfaces.
Bursting and streaming:
USB 2.0 does not support bursting, the low-duration, excessively fast transmission of data, nor does it support streaming, the continuous flow of data between two endpoints once the flow has begun. USB 3.0 supports continuous bursting as well as streaming.
USB 2.0 is a half-duplex technology, meaning that all devices must share a common bandwidth, making overall performance appear subpar. USB 3.0, on the other hand, supports dual simplex communications pathways that collectively imitate full-duplex transmission, where devices at both ends of the cable can transmit simultaneously.
Media access method:
USB 2.0 peripheral devices must wait until polled by the host before transmitting data. USB 3.0 endpoints use an asynchronous transmission mechanism, similar to that of Ethernet, where data is transmitted at will.
The host (computer system) is the only device in the USB 2.0 specification that can control power management. The endpoints are the only devices that can participate in error detection and recovery as well as flow control. USB 3.0 endpoints can all control when they enter low-power mode to conserve power. Error handling and flow control are performed on each link in USB 3.0, not just at the endpoints.
USB 2.0 provides a maximum of 100 milliamperes (mA) of current at low power and 500mA at high power. USB 3.0 provides 150mA and 900mA, respectively, allowing for the direct powering of some of the same component types that FireWire is capable of powering but that USB 2.0 is not.