Superspeed USB Universal Serial Bus 3.0

USB 3.0 is the next major revision of the ubiquitous Universal Serial Bus, the de-facto standard to connect/ charge peripheral to home computers, currently running at 2.0 but this year, consumers will be USB 3.0 starts emerging.   The new specs will be downward compatible.

In a nutshell, USB 3.0 promises the following:

• Higher transfer rates (up to 4.8 Gbps or 480 MB per second)  compared to 0.48 Gbps or 480 Mbps with USB 2.0
• Increased maximum bus power and increased device current draw to better accommodate power-hungry devices
• Reduce charging time to USB 3.0 compliant devices
• New power management features
• Full-duplex data transfers and support for new transfer types
• New connectors and cables for higher speed data transfer…although they are backwards compatible with USB 2.0 devices and computers

The enhancements to USB 3.0 are not just for higher data rates, but for improving the interaction between device and host computer. While the core architectural elements are inherited from before, several changes were made to support the dual bus arrangement, and several more are notable for how users can experience the improvement that USB 3.0 makes over USB 2.0:

• More power when needed
  • 50% more power is provided for unconfigured or suspended devices (150 mA up from 100 mA), and 80% more power is available for configured devices (900 mA up from 500 mA). This means that more power-hungry devices could be bus powered, and battery powered devices that previously charged using bus power could potentially charge more quickly.
  • A new Powered-B receptable is defined with two extra contacts that enable a devices to provide up to 1000 mA to another device, such as a Wireless USB adapter. This eliminates the need for a power supply to accompany the wireless adapter…coming just a bit closer to the ideal system of a wireless link without wires (not even for power). In regular wired USB connections to a host or hub, these 2 extra contacts are not used.
     
• Less power when it’s not needed
  Power efficiency was a key objective in the move to USB 3.0. Some examples of more efficient use of power are:
  • Link level power management, which means either the host computer or the device can initiate a power savings state when idle
  • The ability for links to enter progressively lower power management states when the link partners are idle
  • Continuous device polling is eliminated
  • Broadcast packet transmission through hubs is eliminated
  • Device and individual function level suspend capabilities allow devices to remove power from all, or portions of their circuitry not in use
• Streaming for bulk transfers is supported for faster performance
• Isochronous transfers allows devices to enter low power link states between service intervals
• Devices can communicate new information such as their latency tolerance to the host, which allows better power performance

To paint an accurate picture, not everything in USB 3.0 is a clear improvement. Cable length, for one, is expected to have a significant limitation when used in applications demanding the highest possible throughput. Although maximum cable length is not specified in the USB 3.0 specification, the electrical properties of the cable and signal quality limitations may limit the practical length to around 3 metres when multi-gigabit transfer rates are desired. This length, of course, can be extended through the use of hubs.

Additionally, some USB 3.0 hardware, such as hubs, may always be more expensive than their USB 2.0 counterparts. This is because by definition, a SuperSpeed USB 3.0 hub contains 2 hubs: one that enumerates as a SuperSpeed hub, and a second one that enumerates as a regular high-speed hub. Until the USB hub silicon becomes an integrated SuperSpeed USB + Hi-Speed USB part, there may always be a significant price difference.

[Source Everythingusb]

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