SuperSpeed USB 3.0 FAQ

18 January 2013, Comments: 37

Dubbed SuperSpeed USB, USB 3.0 promises a major leap forward in transfer speeds and capability, while maintaining backwards compatibility with USB 2.0 devices. It may sound straightforward, but a lot has had to change; in this FAQ we will address the most common questions about USB 3.0 and explain in plain English what it all means.

What is USB 3.0?

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USB 3.0 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. It is in fact the first major revamp (following Wireless USB and USB On-the-Go) to stay current with modern demands for connectivity bandwidth.

Fast-forwarding to 2012, USB 2.0 has been firmly entrenched as the de-facto interface standard in the PC world for a decade. Yet there’s still the need for more speed by ever greater bandwidth demand from devices, such as storage, video applications and alike. These applications again drive us to where a couple of hundred megabits per second just isn’t 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 publishing the relevant technical documents necessary to allow developers and hardware manufacturers to begin to develop products around the USB 3.0 protocol.

What are the major USB 3.0 improvements?

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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, such as a monitor or speedy thumb drive, could be bus powered, and battery powered devices that previously charged using bus power could potentially charge more quickly.
  • A new Powered-B receptacle 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

What improvements are made to USB 3.0 cables & hubs?

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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 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 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 plus 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.

What new applications does USB 3.0 enable?

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In a nutshell, any high-bandwidth device that works with USB 2.0 will become better if updated with USB 3.0 support. At the moment, devices that tax the throughput of USB 2.0 include external hard drives, video capture, webcams, video adapters, multi-channel audio interface, and last but not least, Blu-ray burners. High-end flash drives can also push USB 2.0 pretty hard, and oftentimes if multiple devices are connected via a hub, throughput will suffer.

USB 3.0 opens up the laneways and provides more headroom for devices to deliver a better overall user 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 to 10 times the bandwidth available, USB video solutions should work that much better. Single-link DVI requires almost 2Gbps throughput. Where 480Mbps was limiting, 4.8Gbps is more than promising. At such speed, the standard will find its way into some products that previously weren’t USB territory, like external RAID storage systems.

Is faster USB 3.0 already planned?

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A rather surprising announcement was made during CES 2013 that the official USB promoter group has a grand plan to double the speed of USB 3.0 to 10Gbps from the current 4.8Gbps. This is a clear response to the threat of Thunderbolt which is still slow at gaining traction. Though details regarding the so-called USB 3.1 are still sketchy on the technical aspects as of this writing. Existing connectors would still work, yet new cables may not be needed if they are tested capable of operating at 10Gbps. There will even be improved data-encoding efficiency for applications like video and audio. Software stacks and class protocols will also work seamlessly with the amended version of USB 3.0.

What’s certain is that the new specs won’t be completed until the latter half of 2013. The first wave of “double-speed” USB 3.0 products likely won’t hit stores until 2015. Frankly speaking, there’s an 8-year gap between USB 3.0 and 2.0; few really expected a revision just 5 years after the formal introduction of the current standard in 2008.

How does USB 3.0 achieve the extra performance?

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USB 3.0 achieves much higher performance by way of a number of technical changes. Perhaps the most obvious change is an additional physical bus that is added in parallel with the existing USB 2.0 bus. This means that where USB 2.0 previously had 4 wires (power, ground, and a pair for differential data), USB 3.0 adds 4 more for two pairs of differential signals (receive and transmit) for a combined total of 8 connections in the connectors and cabling. These extra two pairs were necessary to support the SuperSpeed USB target bandwidth requirements because the two-wire differential signals of USB 2.0 were not enough.

Furthermore, the signaling method, while still host-directed, is now asynchronous instead of polling. USB 3.0 utilizes a bi-directional data interface rather than USB 2.0’s half-duplex arrangement, where data can only flow in one direction at a time. Without getting into any more technical mumbo jumbo, this all combines to give a ten-fold increase in theoretical bandwidth, and a welcome improvement noticeable by anyone when SuperSpeed USB products hit the market.

Isn’t USB 2.0 fast enough?

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Well, yes and no. USB 2.0 for many applications provides sufficient bandwidth for a variety of devices and hubs to be connected to one host computer. However, with today’s ever-increasing demands placed on data transfers with high-definition video content, terabyte storage devices, high megapixel count digital cameras, and HD video capture and portable media players, 480Mbps is not really fast anymore. 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 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 is a 10x improvement over USB 2.0.

What operating systems support USB 3.0?

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Apple Mountain Lion (10.8) and Microsoft Windows 8 – both shipping in 2012 – came with native USB 3.0 support whereas third-party drivers for Windows 7, Vista, and XP have been available since 2008.

Mountain Lion
Apple has remained silent on the issue of USB 3.0 support in Mac OS X even when the public knows well that Macs will eventually get Ivy Bridge (Intel third-gen Core i CPUs) whose Panther Point platform comes with USB 3.0, for free. For a while, there was an ongoing debate over whether or not Apple will adopt USB 3.0 given its enthusiasm for Thunderbolt. But in mid-June 2012 at WWDC, Apple finally introduced USB 3.0 to its entire line of MacBook Air and MacBook Pro as part of Ivy Bridge processor refresh, and at the same time, OS X Mountain Lion (10.8) was announced to ship in the following month. So, USB 3.0 support on Macs officially begins with Mountain Lion.

LaCie and HighPoint have developed their own USB 3.0 driver for Mac to work with Mac OS X from Leopard (10.5). LaCie solution however only works with its own drives, including FastKey SSD, 2big RAID, Rikiki portable drive.

Windows 8
In October 2012, Microsoft started shipping Windows 8 with built-in USB 3.0 support. The Windows team said it has written a completely new software stack for USB 3.0 rather than adding support on top of the current USB 1.1/2.0 drivers. To save time, work on USB 3.0 software stack actually began way before there were any peripherals so the engineers had to come up with something called virtual USB 3.0 devices for simulations. In retrospect, the team probably has plenty of time since USB 3.0 wasn’t an instant hit and was slow to take off.

Built-in support for USB Attached SCSI Protocol (UASP) will come as well. This will supplement Bulk-Only Transport (BOT) which has its roots in USB 1.1. USAP class driver, which benefits mass storage applications, adds command queuing to deal with multiple concurrent requests and offers lower overheads than BOT protocol. In other words, you will see an even faster transfer rate and lower CPU usage. Only a handful of USB 3.0 drives support USAP as of this writing but on Windows 8, USAP mode will only kick in when the drive interfaces with a USB 3.0 host controller that conforms to xHCI 1.0 specification.

Windows 7, Vista & XP
Intel, Renesas, and other fabs have been updating their own stable USB 3.0 software stacks for Windows 7, Vista, and XP in the last several years. So there’s no reason for us to believe Redmond is in any hurry to bring USB 3.0 support via service packs to the aforementioned Windows platforms.

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

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The good news is that USB 3.0 has been carefully planned from the start to peacefully co-exist with USB 2.0. First of all, while USB 3.0 specifies new physical connections and thus new cables to take advantage of the higher speed capability of the new protocol, the connector itself remains the same rectangular shape with the four USB 2.0 contacts in the exact same location as before. Five new connections to carry receive and transmit data independently are present on USB 3.0 cables and only come into contact when mated with a proper SuperSpeed USB connection.