USB 3.0 規格介紹 高傳輸時代即將展開

USB 3.0 規範實際上只完成了 90% 而已，但因為 AMD 和 Nvidia 兩間公司怕 Intel 挾著身為 USB Implementers Forum 主導者的優勢，在開發晶片組上偷跑，所以聯手揚言如果 Intel 不把規格放出來的話，他們就要另起爐灶，開發自家的 USB 3.0，所以 Intel 只好提早把規格放出來。

新的 USB 3.0 當然和 USB 2.0 相容，但單向傳輸速率高了五倍，而且因為新規格是 Full Duplex 的，因此雙向傳輸合計等於是以前的十倍之多。可惜 USB 產品中用得到 Full Duplex 的應用不多，所以這個全速應該是發揮不出來。另外，因為考量到近代使用 USB 供電、充電的設備愈來愈多，因此 USB 3.0 的供電力也提高到了每個 port 900mA，這樣接 USB Hub 也是方便許多。

No doubt you’re familiar with the Universal Serial Bus – we ranked it as our top PC innovation of all time. But what do you know about the next version of this ubiquitous interface? USB 2.0 (otherwise known as USB Hi-Speed) boosted the original 12Mbps data rate to 480Mmb/s over eight years ago, and now USB 3.0 (dubbed USB Superspeed) is set to multiply that bandwidth tenfold. Intel released the Extensible Host Controller Interface to hardware partners last week after some reported disputes with AMD and Nvidia (who, afraid Intel would have a jump start in incorporating the tech in chipsets, threatened to develop their own USB standard). But how does this affect you? We dug up some new information about USB 3.0, got our hands on the new connectors, and even took a look inside the new cables.
(Edit made to clarify xHCI release)

 

USB 3.0 will be backwards-compatible with USB 2.0

Like the upgrade from USB 1.1 to 2.0, the new 3.0 connectors and cables will be physically and functionally compatible with hardware from the older specs. Of course, you won’t be able to maximize your bandwidth unless you’re using a USB 3.0 cable with Superspeed devices and ports, but at least plugging a 3.0 cable into a 2.0 port won’t blow up your PC. The spec’s compatibility lies in the design of the new connectors. USB 2.0 cables worked off of four lines – a pair for in/out data transfer, one line for power, and the last for grounding. USB 3.0 adds five new lines (the cable is noticeably thicker), but the new contacts sit parallel to the old ones on a different plane, as opposed to being adjacent to them. This means you’ll be able to differentiate between 2.0 and 3.0 cables just by looking at the ends.

 

The maximum speed of USB 3.0 is 4.8Gbps

It’s true: USB 3.0 SuperSpeed will be 10 times faster than the 480Mbps limit of the 2.0 spec. The example Intel likes to give out when talking about the new speed is that transferring a 27GB HD movie to your future media player will only take 70 seconds with USB 3.0, while it would take 15 minutes or more with 2.0. Keep in mind that you’re only going to be able to take advantage of this speed if your portable storage device can write data that quickly. Solid state devices will benefit most from the speed boost, while magnetic hard disks will be limited by their RPM and corresponding read/write speeds. Also, new Mass Storage Device drivers will have to be developed for Windows to take advantage of the spec.

   

Uploads and downloads are kept on separate data lanes

Remember those five new lanes we mentioned earlier? With USB 3.0, two new lanes will be dedicated to transmit data, while another pair will handle receiving data. This not only accounts for the significant speed boost, but also allows USB 3.0 to both read and write at the same time from your portable storage device. In the old spec, the pair of lanes used for data transfer weren’t split between send and receive – they only could handle traffic in one direction. Bi-directional data transfer will be very useful for syncing up information on PDAs and storage backup

 

USB 3.0 will charge more devices, quickerthe host a signal to begin data transfer. This feature will also be backward compatible with USB 2.0 certified devices.

  The spec that Intel released mid-last week is only 90% complete. Ravencraft says that they expect the spec to be finalized by Q4 of this year. Hardware partners are expected to have USB 3.0 controllers designed by mid 2009, and consumers won't see the first end products utilizing the spec until early 2010 (though a late Holiday 2009 push for new products isn't out of the question).

Not only will USB 3.0 cables facilitate faster transfer speeds, but they’ll carry more power, too. The USB-IF recognizes the growing number of portable devices that charge via USB (cellphones, MP3 players, digital cameras), and have bumped the power output from about 100miliamps to 900 milliamps. That means not only will you be able to power more than 4 devices from a single hub, but the increase current will let you charge up heftier hardware as well.

   
One of the mandates of the new spec is more efficient power-usage protocols. USB 3.0 abandons device polling in favor of a new interrupt-driven protocol, which means non-active or idle devices (which aren’t being charged by the USB port) won’t have their power drained by the host controller as it looks for active data traffic. Instead, the devices will send

 

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