YOU MIGHT HAVE noticed a little USB logo on most, if not all of your USB devices that tells you what kind it is, be it bog standard USB, Hi-Speed or now SuperSpeed USB. During today’s USB-IF developer’s conference we put forward the question to the USB-IF, which is the organization behind these logos that certify that your device is USB compliant, with regards to performance testing and what the requirements are.
We were slightly taken back by the answer. The USB-IF doesn’t perform any kind of speed testing at all. For a device to carry the USB logo and get certified, all that is required is that the device meets the interoperability standards and a few other things. Part of the reason for the question was that we’re seeing various motherboard makers touting that they offer the fastest and best implementation on their motherboards and we wanted to see what the USB-IF had to say about it.
The USB-IF suggested that since all motherboard host controllers interface via the PCI Express bus, they should all perform similarly. This is obviously not true for one, as many current generation motherboards, especially those from Intel, are limited to 250MB/s per PCI Express lane, rather than 500MB/s which is the full speed of PCI Express 2.0. USB 3.0 can in theory shift 600MB/s, although real world numbers are more in the region of 250-300MB/s in the fastest of the current implementations. It’s important to note that this is peak performance and not average performance.
This means that the current implementation of USB 3.0 host controllers, not only on many motherboards, but also in most, if not all current notebooks, are going to be bus limited in terms of performance. For most people this is unlikely to be an issue for the time being, but it shows that there’s a big difference as to how the USB 3.0 controller is implemented on the motherboard. However, it’s not just the hardware implementation that is a limiting factor, as were also told that a new USB storage driver should increase the performance of USB 3.0 storage devices. We were told to expect an average performance of 120-130MB/s, but it wasn’t said if this was for read or write operations or both.
USB 3.0 is in fact designed to scale to an insane 25Gbit/s, which is about 3,125MB/s. However, this isn’t even on a roadmap at the moment and it’s not known if this will work on copper or if fibre will be what’s needed once we get to those kinds of speeds. The USB-IF was adamant to point out that USB 3.0 is here today and that Intel’s Light Peak is nothing but a concept at the moment and that they aren’t concerned about it as a competing technology for the time being.S|A
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