Initially, USB provided two speeds (1.5 Mb/s and 12 Mb/s). As PCs became increasingly powerful and able to process larger amounts of data, users needed to get more and more data into and out their PCs. This led to the definition of USB 2.0 specification to provide a transfer rate of 480 Mb/s while retaining backward compatibility.
As technology innovation marches forward, new kinds of devices, media formats, and large inexpensive storage are converging. They require significantly more bus bandwidth to maintain the interactive experience users have come to expect. In addition, user applications demand a higher performance connection between the PC and these increasingly sophisticated peripherals. USB 3.0 SuperSpeed addresses this need by adding an even higher transfer rate to match these new usage and devices.
- SuperSpeed USB 3.0 supports a maximum data rate of 4.8 gigabits per second offering 10x performance increase over Hi-Speed USB (USB 2.0)
- USB 3.0 is full duplex, meaning it can upload and download simultaneously (it's bi-directional); USB 2.0 is only half duplex
- Backwards compatibility with USB 2.0 hi-speed devices
- USB 3.0 has got dual bus architecture means SuperSpeed bus operates concurrently with USB 2.0
- SuperSpeed USB is a Sync-N-Go technology that minimizes user wait-time.
- SuperSpeed USB will provide improved power efficiency. No device polling and lower active and idle power requirements
- USB 3.0 SuperSpeed creates a communication pipeline with host and each device or a "host-directed protocol". The older USB 2.0 Hi-Speed broadcasted packets to all devices.
- Cable makeup: 2 wires for power and ground, 2 for Hi-Speed backward compatibility, 4 wires for the new Superspeed
- Shielded differential pair (SDP, twisted or twinax) is needed for USB 3.0. UTP cable used for USB 2.0 can not be used for USB 3.0
- USB 3.0 cable can be upto 3 meters to maintain SuperSpeed data transfer rates
- USB 3.0 SuperSpeed can handle more power over its cable. 50% more than USB 2.0
- USB 3.0 has dual simplex and asynchronous notifications
- USB 3.0 Standard-A connector has complete compatibility with USB 2.0 Standard-A connector. However, a new receptacle has been created "USB 3.0 Standard-B" which can only accept a USB 3.0 Standard-B device plug.
Fig: USB 3.0 Standard-A Connector
Features | USB 3.0 | USB 2.0 |
Speed | Upto 4.8 Gb/s | upto 480 Mb/s |
Signaling | Dual-simplex four wire differential signaling | Two wire differential signaling |
Data flow | Full duplex | Half duplex |
Power Management | Multi-level which supports idle, sleep, and suspend | Port-level that has two levels of entry/exit latency |
Cable types | Shielded differential pair (SDP) | Unshielded twisted pair (UTP) |
Cable Wires | 8 total | 4 total |
Traffic Flow | Asynchronous | Polled |
Packet Traffic | Explicitly routed | Broadcast to all devices |
