Transfer Rates: USB 2.0 offers 480 Mbps and USB 3.0 offers 4.8 Gbps, which is 10 times faster.
Addition of another physical bus: The number of wires is doubled from 4 to 9. Because the additional wires require more cable and connector space, new connectors were designed.
Power Consumption: USB 2.0 consumes 500 mA while USB 3.0 consumes up to 900 mA. USB 3 devices provide more power when needed, but save power when idle.
More Bandwidth: Instead of unidirectional communication, USB 3.0 uses two unidirectional data paths, one to receive data and the other to transmit, while USB 2.0 can only handle data in one direction at any given time.
Improved Bus Utilization: A new feature has been added (using packets NRDY and ERDY) that lets a device asynchronously notify the host of its readiness.
When data is transferred over USB 3.0 devices, cables, and connectors, the transaction is initiated by the host initiating the request and then the device responding. The device either accepts the request or rejects it. If it accepts, the device sends data or accepts data from the host. If it runs out of buffer space or data, it responds with a not ready (NRDY) signal, telling the host that it cannot process the request. When the device is ready, it sends an endpoint ready (ERDY) to the host, which then reschedules the transaction
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