Table 3. USB evolution
Type
Data Transfer Rate
Category
Introduction Year
USB 3.0
4.8 Gbps
Super Speed
2010
USB 2.0
480 Mbps
High Speed
2000
USB 1.1
12 Mbps
Full Speed
1998
USB 1.0
1.5 Mbps
Low Speed
1996
USB 3.0 (SuperSpeed USB)
For years, the USB 2.0 has been firmly entrenched as the de facto interface standard in the PC world with about 6 billion devices sold, and
yet the need for more speed grows by ever faster computing hardware and ever greater bandwidth demands. The USB 3.0 finally has the
answer to the consumers' demands with a theoretically 10 times faster than its predecessor. In a nutshell, USB 3.0 features are as follows:
•
Higher transfer rates (up to 4.8 Gbps)
•
Increased maximum bus power and increased device current draw to better accommodate power-hungry devices
•
New power management features
•
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.
Speed
Currently, there are 3 speed modes defined by the latest USB 3.0 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 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 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 utilizes the bidirectional data interface, rather than USB 2.0's half-duplex arrangement. This gives a 10-fold increase in
theoretical bandwidth.
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Technology and components
