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Is There A Difference Between USB 3.0 Configurations?

Does The USB 3.0 Controller On Your Motherboard Matter?

A lot of USB connectivity: Thanko's 80-port hub.A lot of USB connectivity: Thanko's 80-port hub.

There are several USB 3.0 controllers on the market. But which is the best? This isn't really something you can determine by transferring a few files to one external device. Rather, you want to go as far as possible to saturate the bus.

USB connectivity is so ubiquitous that many of us are accustomed to running systems with nearly every port populated. This can have a significant impact on performance. For example, the maximum data rate for USB 2.0 is 480 Mb/s, but that’s per controller and is divided amongst all attached devices. Once upon a time, a single USB device couldn't consume all of that bandwidth. Scaling up to two or three, however, certainly could hit the ceiling. Today, it's not difficult at all to butt up against the limits of USB 2.0 with just one external hard drive.

RocketU 1144ARocketU 1144A

One way to overcome the bottlenecks imposed by sharing bandwidth is to employ multiple controllers. That’s the idea behind HighPoint’s RocketU 1144A add-in card. The board maps each of its four USB 3.0 ports to a single ASMedia ASM1042 controller, leveraging an eight-lane PEX8609 switch to deliver 2 GB/s of bandwidth in each direction over a PCI Express x4 slot. That's balanced perfectly to the 500 MB/s In theory, that should provide 500 MB/s of dedicated bandwidth per port, which syncs up well with the 500 MB/s theoretical limit of USB 3.0 (5 Gb/s divided by eight bits per byte, time .8 to account for 8b/10b encoding).

Compare that implementation to what you see built onto motherboards. Gigabyte’s A75-UD4H and Asus’ F1A75-V Pro both facilitate four USB 3.0 ports through the A75 Fusion Controller Hub (FCH). Additional connectivity is provided via the EJ168 (Gigabyte) and ASM1042 (Asus) controllers.

More specifically, the A75-UD4H relies on two EJ168 controllers to support four additional USB 3.0 ports, while Asus employs a single ASM1042 that provides support for two extra ports. However, these third-party solutions are technically less than ideal because two ports need to share the bandwidth provided by a single PCIe x1 lane. In a situation where you have two high-speed devices attached to the same controller, you'd theoretically be bottlenecked. 

Regardless, we’re out to answer two questions:

  1. Is there one USB 3.0 controller that's better than the others?
  2. Do bottlenecks exist when you plug multiple performance-oriented devices into one controller?

To that end, we’re testing the storage performance of various USB 3.0 controllers under the following configurations:

HighPoint RocketU 1144A and AMD A75 FCH:

  • One USB 3.0 device
  • Two USB 3.0 devices
  • Four USB 3.0 devices

Etron EJ168 and ASMedia ASM1042:

  • One USB 3.0 device
  • Two USB 3.0 devices
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