USB 3.0 is faster than USB 2.0, but by how much really?

I'm a bit uncertain by just how much faster USB 3.0 is over USB 2.0. I've read a few articles where it was stated that on paper 3.0 is 10x faster than 2.0, but would never be achieved in the the real world. The "real world" improvement would be more like 3x.

Now, I'm sure this is making several assumptions, such as native USB 3.0 and no hard drive involved in data transfer.

If you are doing a data transfer test with USB 2.0 and USB 3.0, they're both dealing with the exact same environment. If you've got a SATA II (3gb) 5400rpm drive, both speeds will be hampered if the hard drive is involved in a data transfer. Also, USB 3.0 is enabled on my laptop via a USB 3.0 port plugged into an Express Card slot. The device is rated for USB 3.0, 5Gbps, so I don't think it's a bottleneck.

I conducted a test with both and found only a 42% improvement. While still significantly better, it isn't quite as stellar as I'd have expected. In the test I copied the same files from my hard drive to a USB 3.0 enabled external hard drive (also supports USB 2.0).

What I'm trying to understand is if there's another bottleneck somewhere. Does the very fact that I have a SATA II 5400rpm hard drive end up capping USB 3.0 but not USB 2.0, so that the difference is less? Is there another kind of test I can do to bypass any data touching the hard drive? I wonder if I can download a file from the Internet, specifying the external USB 3.0 drive, and that there wouldn't be any caching on my slower internal hard drive to interfere.

You are limited by the write speed of the device you are transfering to. No matter how fast your connection is capable of, it can only transfer data at the speed of the receiving device. The 5 Gb/s speed that you refer to as USB 3.0 speed is a therotecial maximum. You will never see even close to that speed. Typically, transfering with USB 3.0 will be 2-3 times faster than USB 2.0, if the device you are transfering to is capable of accepting data that fast.

cytherian said:

Also, USB 3.0 is enabled on my laptop via a USB 3.0 port plugged into an Express Card slot. The device is rated for USB 3.0, 5Gbps, so I don't think it's a bottleneck.

I see you (bolded part). Expresscard speed (the speed of the communication between the expresscard USB 3 adapter and the laptop's mobo) is a bottleneck for USB 3.0.
Doesn't matter what they say. Expresscard speed is a fixed standard (just like USB 2.0 speed is).

If you had a Expresscard 2.0 slot then it's not a bottleneck (it's fast enough to allow you to link a frigging gaming external graphic card to it without lag), but afaik, Expresscard 2.0 is pretty damn rare (maybe because you can do so overkill things with it).

An article that goes more in depth.

I really doubt HDD read/write speed can seriously impact USB speed. HDDs are significantly faster.

^ Thanks a lot for the link to that article, bobafett. It really sums it up rather nicely, and quite shocking to see just how much slower a USB 3.0 Express Card port is compared to native USB 3.0. Amazing. I will definitely wait for USB 3.0 before even considering a new computer system. :)

If you want speed, an eSata port is the best. Much faster than USB3 although the specs would not suggest that. There must be a lot of overhead with USB3.

Just to confirm what WHS said. Here is a test I ran a while back.