Implementation Differences Compared To USB 2.0
The USB 3.0 specification is similar to USB 2.0 but with many improvements and an alternative implementation. Earlier USB concepts like endpoints and four transfer types (bulk, control, isochronous and interrupt) are preserved but the protocol and electrical interface are different. The specification defines a physically separate channel to carry USB 3.0 traffic. The changes in this specification make improvements in the following areas:
- Transfer speed – Added a new transfer type called Super Speed or SS – 5 Gbit/s (electrically it is more similar to PCIe Gen2 and SATA than USB 2.0)
- Increased bandwidth – Instead of one-way communication, USB 3.0 uses two unidirectional data paths: one to receive data and the other to transmit
- Power management – U0 through U3 link power management states are defined
- Improved bus utilization – a new feature is added (using packets NRDY and ERDY) to let a device asynchronously notify the host of its readiness (no need of polling)
- Support to rotating media – Bulk protocol is updated with a new feature called Stream Protocol that allows a large number of logical streams within an Endpoint
USB 3.0 has transmission speeds of up to 5 Gbit/s, which is 10 times faster than USB 2.0 (480 Mbit/s) before taking into account that the former is full duplex and the latter is half duplex, giving USB 3.0 the potential total bandwidth if utilized both ways to 20 times that of USB 2.0.
Read more about this topic: USB 3.0
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