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I have a portable HDD on USB 3.0, and soon I'll have a 32gb flash drive on USB 3.0 as well.

My motherboard is pretty old - and the next time I'll upgrade it is when I get a new CPU/mobo/ram.

Slots on my mobo:

PCIE X16 - For my GTX 260



I'm considering purchasing a PCI express X1 card like this -

Now the question:

What are realistic (read/write) speeds I'll get in this setup, assuming I have 1 USB 3 device connected at a time, and the bottleneck is the PCIE?

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up vote 2 down vote accepted

Bandwidth for PCIe 1x is 250 [500]* MB/s

  • Note 1 - Since PCI Express is a serial based technology, data can be sent over the bus in two directions at once. Normal PCI is Parallel, and as such all data goes in one direction around the loop. Each 1x lane in PCI Express can transmit in both directions at once. In the table the first number is the bandwidth in one direction and the second number is the combined bandwidth in both directions. Also please note that in PCI Express bandwidth is not shared the same way as in PCI, so there is less congestion on the bus.


USB 3.0 is also known as Super Speed

The new SuperSpeed mode has a transfer rate of 4.8Gbps

Real word speeds of 3.0 will be different depending on the chipmaker implementation, device connected and the chip it uses, and OS


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Ahk. So USB 3.0 has a theoretical speed limit of 625MB/s, PCIE X1 is 250MB/s, and USB 2.0 is 60MB/s. In that case I'll go for it. :) – lelouch Nov 23 '11 at 0:52
Yes it should be much faster than 2.0, post back when you test it. – Moab Nov 23 '11 at 1:08

I hooked a USB 3.0 expansion card up to a PCI x1 slot and I see maximum data transfer speeds of 100 MBps (usually about 50 MBps) and I get a pop-up once in awhile from my Windows 7 OS telling me I can get a faster speed from my (Seagate external USB 3.0) HDD if I hook it to a high speed port (it is already hooked to a USB 3.0 port). Sort of disappointed in the whole deal. -DJ

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100MB/s is likely as fast as the hard drive will go. 50MB/s, you may have other I/O operations on either the source or destination hard drive. Switching to USB 3.0 will get you past the approx. 30MB/s bottleneck of USB 2.0, but your new bottlenecks are the storage devices themselves. – Bob Feb 16 '13 at 14:30
In my job's computer I can read a 64GB Sandisk Extreme at 195MB/s connected to it's USB 3.0. But in my older home computer it only achieves 80 on a "allegedly" Renesas USB 3.0 – skan Aug 24 '15 at 22:19

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