MoBo effective pcie speeds - comparing 2 boards
28 Aug 2015 13:59:46 UTC
Topic 198210
(moderation:
My last MoBo was described as 16x/8x. Its effective speed was of course 8x/8x. I have a new one I just bought used and it says 16x/4x. Does that mean I will get a throughput of 12x/4x or 8x/4x. Both MoBo's are ASRock.
I am running and will be running r9 200series on both boards.
PS. Does it matter if I run a gigabyte card with a sapphire card on the new board? On my old board both cards were from sapphire.
Thanks
merle
What is freedom of expression? Without the freedom to offend, it ceases to exist.
— Salman Rushdie
MoBo effective pcie speeds - comparing 2 boards
)
@merle van osdol
Perhaps this will help a little bit to understand "lanes" connected to the PCIe slots (16x/8x/4x/2x/1x)
http://computer.howstuffworks.com/pci-express1.htm
A "normal" CPU - also such as the latest generation "Intel Skylake" - has 20 lanes, 16 for PCIe, 4 reserved for other interfaces on board. A MoBo with two PCIe slots specified as 16x cannot serve both slots with 16 lanes each (because of over all limitation to 20 lanes). So if two Graphics Cards are connected to "slot 1" and "slot 2" each of them will be feeded through 8 lanes (x8) only.
There are some motherboards on market which fully or pationally are breaking this limitation by integrated "lane switches / PLX bridge (e.g. Gigabyte Z170X-Gaming G1 with expansion to 32 PCIe lanes).
My five cents,
Arthur
I know I am a part of a story that starts long before I can remember and continues long beyond when anyone will remember me [Danny Hillis, Long Now]
RE: A "normal" CPU - also
)
Most normal CPU's I use have 28 or more PCI-e Lanes especially
if they use the MOBO 2011-3 which can have up to 40 Lanes. 16x16x8 config
EDIT Never Mind my PC's are not normal:-)
It is hard to know for sure
)
It is hard to know for sure without knowing the model of the motherboard.
However, motherboard manufacturers will sometimes provide extra slots that tie into the PCH or chipset instead of the CPU PCI-E controller.
For example, the latest Intel Skylake CPU has 16 PCI-E 3.0 lanes available on-die. However, the Intel Z170 PCH which connects to the CPU via a DMI 3.0 link has up to an additional 20 PCI-E 3.0 lanes that can be connected to additional slots and devices.
Jeroen
RE: It is hard to know for
)
Yes, thank you. I failed to mention that it's a 970extreme3 r2.0 MoBo from ASRock. The documentation with the computer and the online info does not clarify what they mean by a 12x/4x setup except that it is useful for the amd Crossfire which of course we don't use. Looks like the latest motherboards are finally expanding their PCI-E capabilities. Nice.
merle
What is freedom of expression? Without the freedom to offend, it ceases to exist.
— Salman Rushdie
The Asrock site
)
The Asrock site says:
"x16 slots" means you can physically plug GPUs into them. "PCIE2 @ x16 mode" means the slot number 2 (probably the one closer to the CPU) provides 16 lanes of the PCIe 2 standard for electrical connectivity. "PCIE4 @ x4 mode" means that slot number 4 only provides 4 of those PCIe 2 lanes, independent of what you plug into the 1st slot. For earlier Einstein apps 4x PCIe 2 would have been catastrophic, but with the new app >=1.52 this should still be OK.
MrS
Scanning for our furry friends since Jan 2002
RE: The Asrock site
)
Thanks furry ape.
merle
What is freedom of expression? Without the freedom to offend, it ceases to exist.
— Salman Rushdie