USB 3.0: Everything You Wanted to Know

USB 3.0 Demystified

When you're in front of your PC, waiting for something to transfer to removable media, seconds can feel like minutes, and minutes like hours. And backups to USB 2.0 appear to crawl along at a snail's pace--so much so that users often become reluctant to perform that essential chore.

Such data-transfer scenarios are where the new Super­­Speed USB 3.0 standard and its theoretical, blazing-fast through­­put of 5 gigabits per second--as promised by the USB Implementers Forum (USB-IF)--will change your life for the better. And if our tests of four new USB 3.0 hard drives from Buffalo Technology, Iomega, Seagate, and Western Digital are indicative, the change will be dramatic.

USB 3.0's impressive speed is its raison d'être, but part of its beauty is its backward compatibility with USB 2.0. You need a new cable and a new host adapter (or one of the new motherboards built to support USB 3.0) to achieve USB 3.0 performance. But you can still use a USB 3.0 device on a USB 2.0 port and achieve typical USB 2.0 performance. You may also use USB 2.0 devices on a USB 3.0 port--though, again, with no gain in speed.

The technology behind USB 3.0 more closely resembles PCI Express than USB 2.0. Backward compatibility comes from clever connector design, and a dual bus. The designers added four data lines and a ground wire for the new USB 3.0 signals, and retained the existing pair of data lines for use with USB 2.0 devices. The two technologies share the existing power and ground wires, but they are otherwise completely separated.

As such, the USB 3.0 connector has design changes to accommodate the extra data lines. If you examine the inside of a type A USB 3.0 port with its familiar rectangular shape closely, you'll see that it shares the same size as a USB 2.0 port as well as the original four USB 1.1/2.0 contacts.

However, the port also has an additional five smaller contacts for the new USB 3.0 lines. When you plug in a 2.0 connector, it uses the four original contacts; when you plug in a USB 3.0 connector, it taps into the other five. Because motherboards and PCs will ship with both USB 2.0 and USB 3.0 ports, their insulating plastic, by specification (to distinguish them) must be bright blue on USB 3.0 ports, but black on USB 2.0 ports. Similar tricks have been used for the type B and mini connectors.

Another potential benefit of USB 3.0: The spec calls for a mere one-third of the power consumption USB 2.0 uses. The creators achieved that by reducing some of the background maintenance re­­quirements of USB; unlike before, with USB 3.0 the interface transmits data only to the link and device that need that info, which allows other attached devices to go into a low-power state when not needed. The change ap­­plies only to the USB bus, not to the power that USB peripherals require or use for their own operation-although getting things done faster ultimately means using less power, as well.

The USB 3.0 revolution is coming, as many SuperSpeed USB 3.0-certified products are now shipping, including host controllers, adapter cards, motherboards (from Asus, Gigabyte, Intel, and others), and hard drives. But it won't be an immediate switch: According to In-Stat Research, it will be 2013 when more than one-quarter of USB products support SuperSpeed USB 3.0.

That slow transition isn't particularly surprising, considering that no compatible peripherals or consumer electronics devices have even been announced so far. Some devices, such as keyboards and mice, won't benefit from SuperSpeed USB's increased performance. Other products, such as digital cameras and camcorders, will; we anticipate seeing USB 3.0 start to appear on this class of de­­vices sometime in 2011.

High Performance

The theoretical improvement in throughput that USB 3.0 offers is certainly dramatic--a 10X jump to 5 gbps over the existing USB 2.0 spec, which maxed out at a theoretical 480 mbps.

But how does USB 3.0 fare in the real world? Pretty darn well, it turns out.

To determine the veracity of the USB-IF's claims, we ran Western Digital's My Book 3.0 1 TB SuperSpeed USB 3.0 drive through our test suite, which in­­cludes batch operations on a large set of small files, transfers of very large files, and a virus scan test that em­­pha­sizes a hard drive's seek speed.

In PCWorld Labs tests, the drive assessed using USB 3.0 consistently proved noticeably faster than when using FireWire 800 (by as much as a third). And we found the USB 3.0 drive to be comparable in speed with eSATA drives (over a SATA-300 interface); the eSATA drives typically edged out the USB 3.0 unit on a couple of our performance metrics.

By comparison, USB 2.0 looked like a dog cart in the Kentucky Derby. Depending on the test, USB 3.0 proved to be up to 3.5 times as fast and always more than double USB 2.0's speed.

In PCWorld Labs power consumption tests, we found that the average power draw at any given time for the USB 3.0 drives was slightly greater than that of USB 2.0 while data was transferring. However, since USB 3.0 does things far more quickly, multiplying the average draw over time shows it doing roughly twice the work per watt.

Beyond performance measurements, USB 3.0 has a huge edge in convenience over eSATA. Unlike eSATA, USB 3.0 was designed with re­­movable storage in mind. It's hot-pluggable--you simply plug in a device, and your operating system quickly adds it to the list of available devices. By contrast, eSATA drives nearly always require a system reboot to appear.

Furthermore, since USB 3.0 is a powered port, you don't necessarily have to run another external power supply to the drive as you normally do with eSATA drives. Most 3.5-inch hard drives, however, require more power than the USB bus can deliver, and those models will still need AC adapters.

Certified USB 3.0

One of the things to look for when buying a USB 3.0 product is the certified SuperSpeed USB 3.0 logo--a label that will ensure that the product you're purchasing truly lives up to the new specification.

At this point, though, expect companies to release USB 3.0 products without official certification or the SuperSpeed logo. An example is the Buffalo Technology HD-HXU3, which was the first drive to market; and La­­Cie's drives, which are in the process of certification, will initially carry LaCie's own logo for USB 3.0 (the company says it plans to put a sticker on the products' box once certification is completed).

One good thing: This time around, you won't have to worry about whether you're really getting the promised speeds. In the transition from USB 1.1 to USB 2.0, the creators of the latter spec wrote it in such a way that products didn't have to communicate at the full 480 mbps in order to be called "USB 2.0." In contrast, for a product to be certified as supporting USB 3.0, it must operate at the full 5 gbps.

Upgrade Possibilities

It's easy to upgrade to USB 3.0 on the desktop: You can buy adapter cards on the aftermarket, move to a motherboard that has USB 3.0 built-in, or choose a drive that includes a card.

With laptops, however, upgrading will be a tougher road. Unless your portable has an ExpressCard slot to accept an adapter, you're not going to be able to add USB 3.0 to the notebook that you have now.

New laptops, though, will be a different story--eventually. So far only HP and Fujitsu have an­­nounced limited USB 3.0 support on laptops. Taiwanese laptop and desktop manufacturer MSI says it won't have USB 3.0 until the third quarter of this year, at the earliest. Product managers for both laptop and desktop makers cite manufacturing concerns such as having chipsets available in large quantities, and the need to test USB 3.0 chipsets, as reasons for the delay.

The Final Word

Speed, backward compatibility, power consumption...USB 3.0 more than lives up to the hype. It's only marginally slower than eSATA, and is far better suited to removable storage.

eSATA may yet pull farther ahead, especially once external enclosures built with 6-gbps SATA (SATA-600) come to market. However, now that USB 3.0 is here, we wouldn't be surprised to see eSATA lose traction to USB 3.0--at least in the general, non-high-performance consumer market. FireWire 800 is in a similar position: Aside from Mac support, FireWire 800 provides no tangible benefit over USB 3.0.

In the end, the real question is, do you want to have the speed of USB 3.0? We certainly do.