Getting Good Speed From USB 3.0
Nearly every motherboard sold today comes with USB 3.0 support (the blue ports in the image above). And, based on our results, we're happy to say that you really don't have to worry about the USB 3.0 controller your board vendor of choice uses on its platforms. Frankly, the devices you plug into a USB 3.0 controller are going to limit performance, not the controller itself. There isn't an individual device we've seen able to push the upper limits of what this standard accommodates; you'd need to push more than 500 MB/s to saturate a PCIe x1 link and the intermediary controller. And even with two of Kingston's fast external SSDs attached to one controller, we still didn't tag that limit.
It doesn't take an engineer to figure out why this is the case, though. Currently, all of the fastest USB 3.0-based external drives employ SATA 3Gb/s SSDs, limiting their peak performance to about half of what the bus can handle. Stepping up to a pair of 6 Gb/s devices hammering USB 3.0 would likely cause more of a jam-up. However, the extra cost for even faster external devices probably wouldn't attract a ton of attention, since they'd be faster than most folks' internal storage subsystems. Perhaps someday soon we'll see SF-2200-based USB 3.0 drives able to push the standard's limits. For now, though, that's pretty unrealistic, meaning that you aren't going to see a difference between USB 3.0 controllers.
The key differentiator between USB 3.0 controllers will come with Windows 8. Microsoft plans to provide native driver support for USB-attached SCSI (UAS), anticipated to support NCQ instructions over USB. As a result, you can expect to benefit from an SSD's ability to reorder operations to take advantage of multi-channel architectures, which generally result in higher performance as queue depth increases.
A simple operating system upgrade won't enable NCQ over USB. In addition to the software driver, proper functionality will require a compatible USB 3.0 controller and client device on the other end. ASMedia's ASM1042 already contains logic that should support UAS, but we don't know the status of AMD's A75 or Etron's EJ168. Things are even less clear at the device-level because we don't know if any of the external peripherals out right now are UAS-ready.
That's future stuff, though. Until we get there, you can go on enjoying the blazing-fast speed of USB 3.0 knowing that, for the most part, it's really hard to saturate the throughput of a single port, and even two ports originating from the same controller deliver reasonable performance. If you're lucky enough to own four of Kingston's fast HyperX Max 3.0 drives and want to plug them into AMD's A75 chipset or HighPoint's RocketU 1144A, you should see comparably-good speed, too.