PCIe Slot Speed - x1 x2 x4 x8 x16

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Re: PCIe Slot Speed - x1 x2 x4 x8 x16

Postby foldy » Wed Jul 01, 2020 7:30 am

Maybe it is because my gtx 1080ti was power limited and so clock speed at 1.5Ghz instead of boost 2.0 Ghz?
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Re: PCIe Slot Speed - x1 x2 x4 x8 x16

Postby Joe_H » Wed Jul 01, 2020 3:28 pm

Sparkly wrote:The E5-2670 has 40 PCIe lanes, so with 2 of them on a board you get 80.
https://ark.intel.com/content/www/us/en ... l-qpi.html

And since the Xenon is server grade, then the motherboard supporting it will most likely also have all 16 PCIe lanes connected to each x16 slot, as opposed to a lot of consumer grade motherboards, where you will often have a x16/x8 configuration, meaning you have a physical size x16 slot, but there are only 8 PCIe lanes connected to it.


You wil have that many PCIe lanes if, and only if, the logic board supports that many. Just because the Xeon processors support that many, there often is no business or technical reason to provide that many to the slots. So many server grade boards only use some of the available lanes from the processors. You have to check the specs on each board beforehand.
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Re: PCIe Slot Speed - x1 x2 x4 x8 x16

Postby MeeLee » Thu Jul 02, 2020 9:02 am

foldy wrote:Maybe it is because my gtx 1080ti was power limited and so clock speed at 1.5Ghz instead of boost 2.0 Ghz?

Most likely.
Handicapping your GPU by 20% (they probably don't really hit a constant 2Ghz), it would perform closer to between a 1660 and a 2060.
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Re: PCIe Slot Speed - x1 x2 x4 x8 x16

Postby MeeLee » Thu Jul 02, 2020 9:06 am

Joe_H wrote:
Sparkly wrote:The E5-2670 has 40 PCIe lanes, so with 2 of them on a board you get 80.
https://ark.intel.com/content/www/us/en ... l-qpi.html

And since the Xenon is server grade, then the motherboard supporting it will most likely also have all 16 PCIe lanes connected to each x16 slot, as opposed to a lot of consumer grade motherboards, where you will often have a x16/x8 configuration, meaning you have a physical size x16 slot, but there are only 8 PCIe lanes connected to it.


You wil have that many PCIe lanes if, and only if, the logic board supports that many. Just because the Xeon processors support that many, there often is no business or technical reason to provide that many to the slots. So many server grade boards only use some of the available lanes from the processors. You have to check the specs on each board beforehand.

Not to mention, dual CPU systems speak to one another via PCIE lanes too.
At least 8 CPU lanes (or more) will be dedicated to just the CPUs communication ring, mostly to share ram with one another.
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Re: PCIe Slot Speed - x1 x2 x4 x8 x16

Postby Joe_H » Thu Jul 02, 2020 1:51 pm

MeeLee wrote:Not to mention, dual CPU systems speak to one another via PCIE lanes too.
At least 8 CPU lanes (or more) will be dedicated to just the CPUs communication ring, mostly to share ram with one another.


No, Xeon processors since 2008 have used QPI for interprocessor communication, that changed to UPI with chips produced starting in 2017. Totally separate bus from PCIe, and the number of QPI/UPI connections available distinguish Xeon processors intended for single, dual, and multi-processor systems.
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Re: PCIe Slot Speed - x1 x2 x4 x8 x16

Postby bruce » Fri Jul 03, 2020 1:59 am

The standard Intel I5 or i7 CPU is generally connected to the system through a 1x connection, even if the iGP is enabled.
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