So, just how fast is this USB 3.0 implementation? To find out, we needed an external drive with a SuperSpeed interface, which Asus conveniently sent along with the U3S6.
This Vantec-branded enclosure houses a Seagate Barracuda 7200.12 500GB hard drive whose peak transfer rates aren't anywhere close to 600MB/s. However, the 'cuda is still one of the fastest mechanical hard drives you can buy. You're going to have to get into multi-drive RAID enclosures to come close to saturating USB 3.0's available bandwidth with today's hard drives.
Note in the picture above that USB 3.0 uses a slightly different B connector type than USB 2.0. The plug is backward compatible with USB 2.0 cables, but a SuperSpeed B connector won't fit into a USB 2.0 B plug.
USB 2.0's A connector type, which is commonly found on motherboard port clusters and in notebooks, is the same in the new generation. You can plug USB 2.0 devices into USB 3.0 ports and vice versa. The SuperSpeed spec also calls for a dual-bus architecture that allows USB 3.0 and 2.0 devices to operate simultaneously at their optimal speeds.
To gauge performance, we plugged the U3S6 into an Asus P7P55D Premium motherboard's secondary PCIe x16 slot. That slot has an eight-lane PCIe gen-two connection to the system's Core i7-870 CPU. We connected the drive enclosure to the U3S6's USB 3.0 port and tested with HDTach. We then ran the same test with the drive connected to the motherboard's USB 2.0 port.
We also yanked the Barracuda hard drive from the enclosure and hooked it up to one of the board's Serial ATA ports to get an idea of the kind of performance an eSATA setup might yield.
USB 3.0 easily outpaces its predecessor, offering up to 3.5 times the throughput of the old Hi-Speed standard in HD Tach's sustained transfer rate tests. The Barracuda 7200.12 isn't capable of transfer rates much higher than 120MB/s, though. Our Serial ATA scores suggest that an eSATA implementation of this drive would be just as quick.
The SATA setup is even faster in the burst speed test, pushing 46MB/s more than SuperSpeed USB. I'm not sure what to make of this result, but it suggests that the NEC controller is hitting a bottleneck, at least when it comes to short burst transfers. Of course, you're still getting much higher burst rates than USB 2.0.
SuperSpeed's higher transfer rates don't cost much in the way of CPU time. HD Tach's margin of error for this test is +/- 2%, and we're well within that range.