[SOLVED] Why does changing the SATA connection slot changes PCIe from x16 to x8?

Abhisek_3

Reputable
Aug 28, 2016
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Hi! Previously I posted a thread here for a solution to this problem of mine. I found out that if I change my SSD's connection from the 4th SATA port to the 2nd SATA port, the GPU starts running at x16 3.0 but if I use the 4th port, it runs at x8 3.0 . Can you please tell me why this is happening? It is preventing me from buying another SSD which is really important for me.

Ryzen 3600
MSI B450M Pro-VDH Plus
16 GB 8x2 3200 CL16 ADATA XPG RAM
RADEON R9 270X
1TB HDD + 240 GB SSD

Now, as my GPU is pretty old for a Ryzen 3000 PC, x8 3.0 or x16 3.0 does not make a lot of differences, but it's curiosity you know!! Please tell me what's wrong. Thank you!
 
The PCIe steering options for that board are 'stealing' 8 PCIe lanes going to that slot to feed the SATA ports. Very wasteful of bandwidth but to my knowledge PCIe lane width options to a slot only come in x1, x2, x4, x8 and x16 so no x12.

Most often they only share bandwidth for a couple of the SATA ports on B450 boards, with at least 4 others having a dedicated connection to the chipset and therefore not shared. Try moving the SATA drive to different ports on the motherboard if you have them available.

If you must use that port it shouldn't impact GPU performance to any great degree in games. You could run some tests of your own with 3dMark Firestrike or Timespy. There are doubtless some GPU compute applications that could be impacted but I'm not sure what they are.
 
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Spaceghaze

Proper
Oct 17, 2019
159
12
115
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Im thinking this has something to do with available PCI lanes. Mobo's will disable sata ports, or PCIE ports depending on what you have connected at the same time. Check the mobo's manual. It should specify what is disabled if you connect this or that.
 
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The PCIe steering options for that board are 'stealing' 8 PCIe lanes going to that slot to feed the SATA ports. Very wasteful of bandwidth but to my knowledge PCIe lane width options to a slot only come in x1, x2, x4, x8 and x16 so no x12.

Most often they only share bandwidth for a couple of the SATA ports on B450 boards, with at least 4 others having a dedicated connection to the chipset and therefore not shared. Try moving the SATA drive to different ports on the motherboard if you have them available.

If you must use that port it shouldn't impact GPU performance to any great degree in games. You could run some tests of your own with 3dMark Firestrike or Timespy. There are doubtless some GPU compute applications that could be impacted but I'm not sure what they are.
 
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