USB 3.0 FAQ: All Your Questions Answered!

Alex Castle

After this years CES, it's clear that USB 3.0 is here to stay. Wtih a tidal wave of consumer devices looming on the horizon, we've decided to help clear up confusion about USB 2.0's successor. Here's all the information you need to know about USB 3.0 , organized into a brief FAQ.

How is USB 3.0 different from USB 2.0?

USB 3.0 features a number of features not seen in USB 2.0. The most important of these is the "SuperSpeed" bus--two additional pairs of wire which allow for significantly faster transfers than before, with full duplex transfers. These additional connections require a different, larger form factor for USB 3.0 plugs. USB 3.0 also improves on the power-management capabilities of USB 2.0, offering advanced efficiency features, as well as the ability to provide more power to USB 3.0 devices. About the only drawback to USB 3.0 is that the maximum cable length for high speed transmission is likely to drop to around 10 feet, from 15 feet with USB 2.0.

Is USB 3.0 backward compatible with earlier USB standards?

Yes it is. A USB 2.0 device will be able to plug into a USB 3.0 port and will work just fine. Also, a standard A USB 3.0 plug can be inserted into a USB 2.0 A port, operating at USB 2.0 speeds. Other USB 3.0 plugs, however, are larger than their USB 2.0 counterparts, and therefore cannot be used with older-generation ports.

Just how fast is USB 3.0?

USB 3.0 boasts theoretical transfer rates of up to 4.8 Gbps, or 600 megabytes per second--10 times the maximum transfer rate of USB 2.0. This would, ideally, allow you to transfer a 25GB HD movie in about 40 seconds. Pretty fast, huh?

Unfortunately, the theoretical maximum is just that--theoretical. USB 2.0 devices rarely ever reached much more than 50% of the maximum transfer rate, and it's unlikely that USB 3.0 will either. A more realistic estimate, then, is that USB 3.0 will allow transfer at up to 300-400 megabytes per second. At that rate, it would take 60-80 seconds to transfer that same 25 GB HD movie from before.

USB 3.0 hardware is still in its infancy, of course, so even 300 MB/s sustained isn't attainable yet. So far, USB 3.0 transfers top out at around 200 MB/s when using a fast external SSD. Expect that to go up in the not-so-distant future, though.

What does "full-duplex data transfers" mean?

Data transfer is full duplex if it can handle data flowing in both directions (upload and download, for instance) simultaneously. A half duplex connection can only send data in one direction at a time. Think of a walkie-talkie, where you can only hear the other person as long as you're not transmitting, yourself.

Because the SuperSpeed bus uses two differential pairs to transfer data, it can transfer in both directions at the same time, making it full duplex, unlike USB 2.0.

What are USB 3.0's power advantages?

USB 3.0 includes several advances in the way it handles power to external devices.

For one, it increases the power available for devices to use. In low power mode, USB 3.0 provides 150 mA, an increase from 100 mA in USB 2.0. In high-power mode, USB 3.0 provides up to 900 mA, up from 500mA in USB 2.0. These power increases mean faster charging of USB devices, and more USB peripherals that can be run without an AC power adapter.

Further, the spec offers new power-conserving options, including new power states, such as idle and suspend. These allow devices to receive less power when they don't need it. Also, since USB 3.0 no longer uses active, continuous polling of connected devices, peripherals won't have their batteries depleted as fast.

What kind of USB 3.0 devices are available now?

At CES 2010, 17 consumer USB 3.0 devices were announced, including hard drives, motherboard, laptops, and controller cards. Expect to see lots more in the coming months.

What hardware do I need to use a USB 3.0 device?

To use a USB 3.0 device, you'll need a USB 3.0 controller. If your motherboard doesn't have a built-in USB 3.0 controller (and unless you upgraded your mobo VERY recently, it doesn't) you'll need a USB 3.0 controller card, which take up a PCI-e slot, and are available online for around $30. For the laptop crowd, USB 3.0 ExpressCards are also available. Some USB 3.0 hardware is available in a "starter kit" bundle, which includes a controller card.

What software (drivers) do I need to use a USB 3.0 device?

So far, USB 3.0 drivers aren't included in Windows 7, and there's no word on exactly when or if they will be. You'll have to install third party drivers to use your USB 3.0 hardware, which should be provided by your controller card/motherboard manufacturer.

Did we miss anything? If you've got your own questions, leave them below in the comments. We'll forward them to our USB expert and get back to you with the answer!

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