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• Full-duplex data transfers and support for new transfer types
• Backward USB 2.0 compatibility
• New connectors and cable
The topics below cover some of the most commonly asked questions regarding USB 3.0/USB 3.1 Gen 1.
Speed
Currently, there are 3 speed modes defined by the latest USB 3.0/USB 3.1 Gen 1 specification. They are Super-Speed, Hi-Speed and Full-
Speed. The new SuperSpeed mode has a transfer rate of 4.8Gbps. While the specification retains Hi-Speed, and Full-Speed USB mode,
commonly known as USB 2.0 and 1.1 respectively, the slower modes still operate at 480Mbps and 12Mbps respectively and are kept to
maintain backward compatibility.
USB 3.0/USB 3.1 Gen 1 achieves the much higher performance by the technical changes below:
• An additional physical bus that is added in parallel with the existing USB 2.0 bus (refer to the picture below).
• USB 2.0 previously had four wires (power, ground, and a pair for differential data); USB 3.0/USB 3.1 Gen 1 adds four more for two pairs
of differential signals (receive and transmit) for a combined total of eight connections in the connectors and cabling.
• USB 3.0/USB 3.1 Gen 1 utilizes the bidirectional data interface, rather than USB 2.0's half-duplex arrangement. This gives a 10-fold
increase in theoretical bandwidth.
With today's ever increasing demands placed on data transfers with high-definition video content, terabyte storage devices, high megapixel
count digital cameras etc., USB 2.0 may not be fast enough. Furthermore, no USB 2.0 connection could ever come close to the 480Mbps
theoretical maximum throughput, making data transfer at around 320Mbps (40MB/s) — the actual real-world maximum. Similarly, USB
3.0/USB 3.1 Gen 1 connections will never achieve 4.8Gbps. We will likely see a real-world maximum rate of 400MB/s with overheads. At this
speed, USB 3.0/USB 3.1 Gen 1 is a 10x improvement over USB 2.0.
Applications
USB 3.0/USB 3.1 Gen 1 opens up the laneways and provides more headroom for devices to deliver a better overall experience. Where USB
video was barely tolerable previously (both from a maximum resolution, latency, and video compression perspective), it's easy to imagine
that with 5-10 times the bandwidth available, USB video solutions should work that much better. Single-link DVI requires almost 2Gbps
52 Technology and components