USB 3.0: The New Speed Limit

While SuperSpeed's peak speed is 5Gbit/sec., it will drop to a slower speed on occasion -- for example, when it moves data into and out of older devices or when it's being used with a too-long cable.

On top of faster data speeds, USB 3.0 provides up to 150 milliamps (mA) of electricity -- 50% more than USB 2.0 -- to an unconfigured device while the computer it's connected to is finding and loading its needed software. Once the device has been configured and accepted by the computer's operating system, USB 3.0 can deliver 900mA to the device, compared with USB 2.0's 500mA. This should be more than enough to power a hard drive or a camcorder -- or even a USB device (such as a monitor or a projector) that needs more power than is available via a USB 2.0 port.

USB 3.0 offers power conservation as well. While USB 2.0 is either on or off and wastes power when it isn't being used, the new spec comes with three levels of power use that draw progressively less power.

But be aware that first-generation USB 3.0 implementations are power-hungry. The Lenovo ThinkPad W510 that I used for testing ran for 2 hours 19 minutes while continuously playing music from a USB 3.0 external drive -- and ran for an additional 34 minutes when it used a USB 2.0 port.

How we tested

To gauge the abilities of the USB 3.0 spec, I connected each device to a Lenovo ThinkPad W510 that came with an Intel Core i7 processor, 8GB of RAM and a 500GB hard drive. It also has four USB ports: two USB 3.0, one USB 2.0 and one combo USB 2.0/eSATA.

Of course, the first round of USB 3.0 devices will be mostly working off of computers that still offer only USB 2.0 -- either using the 2.0 ports or using adapters that will, hopefully, bring the system up to USB 3.0 specs. I tested this by using a Fujitsu LifeBook A6220, which has a 2-GHz Core 2 Duo processor, 3GB of RAM, a 15.4-in. screen and four USB 2.0 ports. I connected each USB 3.0 device to its USB 2.0 port and then to each of two USB 3.0 ExpressCard controllers: the StarTech 2 Port ExpressCard SuperSpeed USB 3.0 Card Adapter ($50) and the USB 3.0 ExpressCard adapter that came with the Seagate BlackArmor drive.

To evaluate the speed of the three USB 3.0 devices, I used PassMark's DiskMark software, which is part of the PerformanceTest suite. The tests include:

* Sequential Read: The software creates a large test file on the external drive, and the data is read sequentially from beginning to end by the system.

* Disk Sequential Write: The software creates a large test file, and the data is sequentially written on the external hard drive.

* Disk Random Seek RW: The software creates a large test file on the external drive, and the data is read randomly. After a seek is performed to move the file pointer to a random position in the file, a 16KB block is read or written on the drive. Then the test is repeated until all the data is transferred.

* DiskMark: This weighted average score of the other tests gives a good indication of the drive's overall performance in real-world situations.

I also took an 8.45GB folder containing 1,450 files and timed how long it took to transfer them between the system and the drive. Between runs, I emptied the system's Recycle Bin.

To see if USB 2.0 devices work as promised with USB 3.0 hardware, I put together a group of 10 old and new USB 2.0 devices, including an optical drive, mouse, webcam, external hard drive, video camera, keyboard, speakers, SD card, USB key and media player. I plugged them into each of the three controllers, watched to see if they automatically connected and verified that they were working. All passed the test.

Finally, to see how the new hardware affects battery life, I played an uninterrupted stream of music from an external USB 3.0 hard drive on the ThinkPad W510 while using PassMark's BatteryMon to monitor how quickly the system's 9,500mAh battery drained. I did this using the drive with both USB 3.0 and 2.0 and compared the results.

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