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I'm looking for an adaptor that will let me use a USB 3 port as a gigabit ethernet port. This is proving surprisingly hard to find! Is there some reason why this product is either unavailable or very obscure? Is there an online shop (US/Canada) where I can buy such an item? Newegg, TigerDirect, NCIX, etc. do not seem to carry such an item. I find this surprising since it will provide at least double the bandwidth (possibly quadruple) compared to a USB 2 to Gbit adaptor.

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Firstly, no gigabit adapter plugged into a network will get anywhere near the maximum speed. USB 2 provides a theoretical maximum that is "good enough". For what it's worth, I have a USB 2 / ethernet adapter and it's good enough for me. I see around 200 - 250Mbps. – Randolph West Jan 21 at 3:27
@Randolph West: I've found that USB2 tends to max out at about 30MB/s for drives; this agrees with your findings for the ethernet adaptor. Tom's Hardware got speeds of about 111MB/s on a gigabit network (compared to the theoretical maximum of 125 MB/s). My drives aren't that fast (yet), but they're at least twice 30MB/s, so it's worth it for me to use USB 3. – intuited Jan 21 at 4:01
Shopping recommendations are off-topic according to the FAQ. – techie007 Jan 21 at 4:20
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@techie007: Duly noted. The main point of the question is to ask why they are difficult to find, so the question is I think still valid. – intuited Jan 21 at 4:41
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Possible reasons:

  • USB 3.0 is relatively new.

  • Gigabit ports have been standard on motherboards for a while (some even have two) - so it's not like it was in the 1990's where a network adapater was virtual guaranteed to be an add-on item for a nPC.

  • USB 1.1 and 2.0 (and possibly to some extent 3.0, not sure) are CPU driven interfaces - great for convenience but bad when you want the maximum performance from a device such as a hard drive or a network adapter - no one usually tries to use USB for fast networking. Many who would need such an additional interface would install a PCI/PCIe card.

That being said I'm sure one will pop up eventually.

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I've not noticed high CPU usage when accessing a USB hard drive. Are you saying this should be the case? – intuited Jan 21 at 17:39
@intuited CPU usage from USB data transfer is typically in the low single digit percentages. What you mainly get is extra latency. The USB controller can't directly read/write data to memory or to disk. Instead, every time it receives a new chunk of data or finishing sending the one it was working on it has to ask the CPU to transfer data to/from the rest of the computer for it. Because the CPU can't respond instantly to the request there're frequent smaller pauses in USB data transfer. This is why USB2 maxes out at about 65-75% of its theoretical speed. – Dan Neely Feb 17 at 19:55
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