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What is USB 3.0
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Post by Peter Hall
with LA Cloud Suppliers, LLCUSB 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. 2. Isn't USB 2.0 fast enough?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, 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. 3. 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:
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. 4. Will my existing peripherals still work? How will they co-exist?
5. Where are those SuperSpeed USB 3.0 products?
It is important to note that NEC (now Renesas Electronics) and Fresco Logic are the only fabs to produce xHCI USB 3.0 host silicons as of this writing (October 2010). Until Intel, nVidia and AMD start bundling USB 3.0 as part of their motherboard chipset, companies interested in equipping USB 3.0 on their systems will have to source from said fabs for the chipsets. Here's a list of commercially available SuperSpeed USB products:
External Desktop USB 3.0 Hard Drives
Portable USB 3.0 Hard Drives
USB 3.0 Drive Docks & Adapters
USB 3.0 RAIDs
USB 3.0 Flash Drives
USB 3.0 Solid-state Drives
Optical Media Drives
Multimedia devices
Networking
USB 3.0 adapter cards & hubs
USB 3.0 Products Reportedly in the Works
6. What is the future for USB 2.0?
By 2010, computer motherboards should start to come equipped with USB 3.0 ports supplementing USB 2.0 ports. USB 3.0 adapter cards will likely play a large role in driving the installed base of USB 3.0 ports up, but as SuperSpeed-enabled ports become standard on new PCs, device manufacturers will be further motivated to migrate to the new standard. In time, USB 2.0 may be phased out as was USB 1.1, but
for now and the foreseeable future, USB 2.0 isn't going anywhere. 7. What operating systems support USB 3.0?
SuperSpeed support for Windows XP is unknown at this point. Given that XP is a seven year old operating system, the likelihood of this happening is remote, as Microsoft in our opinion, will have to focus on the biggest bang for the buck applications. With the open-source community behind it, Linux will most definitely support USB 3.0 once the xHCI specification is made public. Currently available under non-disclosure agreement in version 0.95 (a draft specification), organizations are forbidden to ship code because it might reveal or imply what is in the specification. Once that hurdle is out of the way, the Linux USB stack would have to be updated to add support for USB 3.0 details such as bus speed, power management, and a slew of other significant changes detailed in the USB 3.0 specification. As is customary, Apple remains silent on the issue of SuperSpeed USB support in MacOS X. Our opinion is that if USB 3.0 realizes the promise of plug and play simplicity like USB 2.0 with dramatically increased speeds, the market for SuperSpeed devices will take off, and Apple will follow the trend. Whether or not this signals a threat to Firewire is not known, but you can be sure that Apple will need to support SuperSpeed if the rest of the industry adopts this interface standard. Given the iterative nature of any software release,
USB 3.0 O/S support will come in stages and phases, where initial support may be buggy, slow, or lacking in some features.
Over time, these bugs will be ironed out, but expect some growing pains as systems migrate and the development teams struggle
to catch up to the high expectations of the computing community at large. We will get there, but it will take time. Anyone
remember how buggy and unstable USB support was in the MacOS in all versions of OS 8 and OS 9 before OS X 10.2 arrived? 8. What new applications does USB 3.0 enable?
High end flash drives can also push USB 2.0 pretty hard, and oftentimes if multiple devices are connected via 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 5-10 times the bandwidth available, USB video solutions should work that much better. Single-link DVI requires almost 2Gbps throughput. Where 480Mbps was limiting, 5Gbps is more than promising. With
its promised 4.8Gbps speed, the standard will find its way into some products that previously weren't USB territory, like
external RAID storage systems. (Though, there are already plenty of USB-only RAID solutions (e.g. LaCie HDD Max, WD My Book Mirror despite being limited by the interface.) 9. How does USB 3.0 compare to competing interfaces (i.e. eSATA, FireWire 3200, ExpressCard 2.0)?
In late 2007, the 1394 Trade Association announced Firewire 3200, called "S3200", that builds upon the existing Firewire 800 standard that was released in 2002. Utilizing the very same connectors and cabling that is required for Firewire 800, S3200 is basically a drop-in replacement once the internal system components are updated in devices. To date, S3200 has not gained much traction, even in traditional Firewire markets such as digital video. Firewire's main claim to fame is that it is a highly efficient peer-to-peer, full-duplex, non-polling data communications protocol with very low overhead. Firewire delivers much higher actual throughput than USB 2.0, and can achieve much closer to its theoretical 800Mbps data rate than USB. Where Firewire 800 can deliver sustained data transfers of around 90MB/s, USB 2.0 hovers more around 40MB/s. It remains to be seen what impact S3200 will have on the computing landscape. eSATA, or External SATA, was brought to market in 2004 as a consumer interface targetted directly at an external storage market crowded with USB 2.0 and Firewire solutions. It successfully address the issue of the interface bottleneck, and allowed fast hard drives to fully realize their performance potential when located external to a server or PC. eSATA supports a data rate of 3.2Gbps, which is more than enough for the fastest hard drives, which can transfer about 120MB/s, easily better than USB 2.0 and significantly better than Firewire 800. eSATA is not without drawbacks, however. Cable length is limited to a mere 2m, it cannot supply power to devices connected on the eSATA bus, and the connectors are neither small nor terribly suitable for consumer devices where aesthetics are important. Over the last several years, eSATA has steadily eroded both USB and Firewire market share in the data storage space, although its applications are limited, and really not well-suited to the portable device market. ExpressCard 2.0 was released practically the same day as the USB 3.0 specification (November 2008) and promises to significantly enhance the ExpressCard standard for the increased speed requirements of today's mobile technologies. Closely tied to both the PCI Express and USB 3.0 specifications, ExpressCard 2.0 supports a variety of applications involving high throughput data transfer and streaming. Maintaining backwards compatibility with the original ExpressCard specification, the hot-pluggable interface standard for I/O expansion in smaller form-factor systems will by definition co-exist with the world of USB 3.0 devices.
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