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Will I get full speed of USB3 using PCi 2 slot?

Last response: in Motherboards
October 26, 2011 3:56:02 PM

Hi I have purchased a USB 3 Pci2 card.

What I want to know is will I get the full speed of USB 3 with PCi2?

Will I have any bottlenecks and what is the max throughput of PCi2?

a c 121 V Motherboard
October 26, 2011 4:38:23 PM

You will be media limited far before you saturate the pipeline of a PCIe 2.0 bus.
October 26, 2011 5:44:53 PM

A single x1 PCI-E 2.0 lane oscillates at 5 GHz, and
each byte has one extra start bit and one extra stop bit,
in addition to 8 data bits, OR 10 bits per byte.

Thus, 5 GHz / 10 = 500 Megabytes per second
in each direction (max bandwidth) per PCIe 2.0 lane.

USB 3.0 is 10 TIMES the speed of USB 2.0,
or 10 x 480 Megabits per second = 4.8 Gb/sec.

Again, each transmitted byte has a start and stop bit + 8 data bits.

Thus, 4.8 Gbps / 10 = 480 Megabytes per second.

So, the limiting factor is the USB 3.0 bandwidth (480)
not the PCI-E 2.0 bandwidth (500).

Of course, controller efficiency is a factor too,
but no controller can exceed the rated max bandwidth.

Hope this helps.