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What is PCI Express x4 in x8?

Last response: in Systems
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June 4, 2011 7:12:05 PM

Supermicro sells server motherboards (see x8st3-f) that describe the PCIE slots as "PCI-E 2.0 X8 on X16" and "PCI-E 2.0 X4 on X8".

What does this mean?

Thanks

More about : pci express

a b B Homebuilt system
a c 147 V Motherboard
June 4, 2011 8:37:23 PM

It means that the PCI-Ex16 slot only has a throughput of a x8 slot and one of the PCI-Ex8 slots only has a throughput of x4. PCIe 2.0 has a throughput of 500MB/s per lane, so a PCI-Ex16 slot should have a throughput of 8GB/s and a PCI-Ex8 slot should have a throughput of 4GB/s. With this motherboard, however, the PCI-Ex16 slot is cut down to x8 so only 4GB/s (as opposed to 8GB/s). The one PCI-Ex8 slot that is cut down to x4 only has 2GB/s throughput.

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