SuperSpeed USB 3.0 FAQ

Updated in November 2011

USB 3.0 (following Wireless USB) is the next major revision of the ubiquitous Universal Serial Bus, created in 1996 by a consortium of companies led by Intel to dramatically simplify the connection between PC and peripherals. Fast forwarding to 2012, USB 2.0 has been firmly entrenched as the de-facto interface standard in the PC world for a decade, and yet still the need for more speed by ever greater bandwidth demands again drive us to where a couple of hundred megabits per second is just not fast enough.

In 2007, Intel demonstrated SuperSpeed USB at the Intel Developer Forum. Version 1.0 of the USB 3.0 (confusing, isn't it?) specification was completed on November 17, 2008. As such, the USB Implementers Forum has taken over managing the specifications and publishes the relevant technical documents necessary to allow developers and hardware manufacturers to begin to develop products around the USB 3.0 protocol. This FAQ attempts to answer the most common questions we receive from readers like you regarding the next gen. interface.

Speed
Q: How fast exactly are these USB 3.0 drives?

Q: How does USB 3.0 achieve the extra performance?

Q: Isn't USB 2.0 fast enough?

Applications
Q: What new applications does USB 3.0 enable?

Q: Where are those SuperSpeed USB 3.0 products?

Compatibility
Q: What operating systems support USB 3.0?

Q: Will my existing peripherals still work? How will they co-exist?

Comparison
Q: How does USB 3.0 compare to competing interfaces?

USB MILESTONES

2012	Intel integrates USB 3.0 into chipset Windows 8 begins USB 3.0 support
2009	NEC ships first USB 3.0 silicon SuperSpeed USB logo introduced Linux begins native USB 3.0 support
2008	USB 3.0 specs released
2005	Wireless USB 1.0 specs released
2002	Windows XP SP1 supports USB 2.0 natively
2001	USB OTG specification released.
2000	USB 2.0 specs released USB started to gain reputation as a mainstream bus technology
1998	Apple shipped iMac with USB ports USB 1.1 specification released
1997	USB-IF membership increased to over 400 companies Over 500 USB products were in development worldwide
1996	USB 1.0 specs released First USB product introduced. First USB Plugfest compliance workshop held.
1995	USB Implementers Forum (USB-IF) formed with an initial membership of 340 companies Intel introduced the first USB silicon.
1994	USB core companies assembled

Improvements
In a nutshell, USB 3.0 promises the following:

Higher transfer rates (up to 4.8Gbps)
Increased maximum bus power
New power management features
Full-duplex data transfers
Support for new transfer types
Backward USB 2.0 compatibility
New connectors and cables

The enhancements to SuperSpeed USB 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

Cable Length & Hubs
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 or signal extenders.

Additionally, some SuperSpeed USB hardware, such as hubs, may always be more expensive than their USB 2.0 counterparts. This is because by definition, a SuperSpeed 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. Some unofficial discussion has surfaced on the web with respect to fiber-optic cabling for longer cable length with USB 3.0. The specification makes no mention of optical cabling, so we conclude that this will be defined in a future spec revision, or left to 3rd party companies to implement cable extension solutions for SuperSpeed USB.

Host Controllers
In the beginning of 2009, only Renesas Electronics was producing USB 3.0 host controllers. As of late 2011, a number of fabs have jumped onto the bandwagon in mass producing USB-IF certified xHCI USB 3.0 host chips. Until Intel starts bundling USB 3.0 as part Ivy Bridge CPU refresh in mid-2012, companies interested in acquiring the new speedy interface will have to source from said fabs for their chipsets. AMD, on the other hand, has already begun supporting USB 3.0 in their Fusion APUs beginning Q2 2011. Here's a performance 7-way USB 3.0 host controller round-up for those who are interested in which brand of USB 3.0 silicon is the best performer.

Here's a list of known USB 3.0 host controllers: