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1. Introduction
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 host computer and peripheral devices. Fast forwarding to 2009, USB 2.0 has been firmly entrenched as the de-facto interface standard in the PC world for years (with about 6 billion devices sold), and yet still the need for more speed by ever faster computing hardware and ever greater bandwidth demands again drive us to where a couple of hundred megabits per second
In a nutshell, USB 3.0 promises the following:
1. Higher transfer rates (up to 4.8Gbps)
2. Increased maximum bus power and increased device current draw to better accommodate power-hungry devices
3. New power management features
4. Full-duplex data transfers and support for new transfer types
5. New connectors and cables for higher speed data transfer...although they are backwards compatible with USB 2.0 devices and computers
2. History of USB 3.0
USB 3.0 is the next stage of USB technology. Its primary goal is to provide the same ease of use, flexibility, and hot-plug functionality but at a much higher data rate. Another major goal of USB 3.0 is power management. This is very important for “Sync & Go” applications that need to trade off features for battery life.
Chipsets are expected to begin shipping in 2010, with broad deployment in 2011. A variety of USB 3.0-based products including PC motherboards, hard drives, PCI Express (PCIe) add-on cards, and cameras were showcased in industry events in 2009, and more products are expected to be released in early 2010.
USB 3.0 heralds an all-new wave of application usage models and is expected to deliver actual throughput greater than 3 Gbits/s (raw signaling speed of 5 Gbits/s), which is more than 10 times higher than that of Hi-Speed USB. Initially, USB 3.0 will target the PC market and devices requiring high rates and volumes of data transfer, such as external storage, consumer electronics, and communications products with increasing amounts of storage.
3. How does USB 3.0 achieve the extra performance?:
USB 3.0 achieves the 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?:
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, terrabyte storage devices, high megapixel count digital cameras, and multi-gigabyte mobile phones 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 320 Mbps - the actual real-world maximum. Similarly, USB 3.0 connections will never achieve 4.8Gbps, but even 50% of that in practice is almost a 10x improvement over USB 2.0.
4. What other improvements does USB 3.0 provide?:
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 page 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 page 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 page 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 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.
Will my existing peripherals still work? How will they co-exist?:
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 transitted data independently are present on USB 3.0 cables and only come into contact when mated with a proper SuperSpeed USB connection.