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PCIe and DMI constraints on 12th Gen. CPUs

Budsy
Beginner
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Hi, I want to upgrade my PC but I am confused about how the 12th  Gen CPUs handle the PCIe lanes.

 The 16 lanes of PCIe 5.0 are all allocated to the “graphics card” slots on the CPU connection.

Given that affordable PCIe 5.0 devices are years away,  I am wondering why these busses weren’t left at PCIe 4.0 , with the focus put on improving the DMI to V.5.0 .

It seems to me that DMI bandwidth is a much more pressing need than providing PCIe 5.0 for devices that don’t yet exist.

Is there a strong engineering reason for the current configuration?

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David_G_Intel
Moderator
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Hello Budsy


Thank you for posting on the Intel️® communities. To give you the most accurate information, are you looking for a specific 12th gen model?


Regards, 

David G 

Intel Customer Support Technician 


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Budsy
Beginner
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Hi David, Thanks for your reply.

I am particularly looking at the 12700 and 12900.

Here is the diagram I am looking at.

 

Budsy_0-1643531103511.png

 

 

The DMI has 8 lanes which are supposed to handle everything coming through the PCH (Z690).

The PCH inputs can apparently extend to 12x PCIe 4.0 lanes  +  16x PCIe 3.0 lanes  + 8 x SATA  + all USB + all wifi + all ethernet + other processor overheads;  all this being processed through the Z690 chip.

You can see that just the 12x PCIe 4.0 lanes alone (if all active) would be enough to cause a bottleneck at the DMI. Given the extensive multi-tasking that the Z690 chip has to do, even in everyday use, it is apparent that connecting any SSDs via this route is sub-optimal.

Yet , despite this congestion, the diagram shows direct connection to the CPU of 16 x PCIe 5.0 lanes (presumably for a video card or such,  that doesn’t yet exist) +  4 x PCIe 4.0 lanes (presumably to accommodate one  good SSD).

So the 16 x PCIe 5.0 lanes seem to be a practical waste at this point in time.

 Do any mother boards allow two M.2 SSDs to connect via the direct CPU bus?

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David_G_Intel
Moderator
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Thank you for the feedback @Budsy. Let me investigate this request and I will post the updates on the thread.


Regards, 

David G 

Intel Customer Support Technician


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David_G_Intel
Moderator
3,546 Views

Hello @Budsy, here is some information that might be helpful for your request:

  1. Regarding the PCIe 5.0 vs 4.0 question, there is not a specific reason since that is the way the product was designed.
  2. Regarding the bandwidth question, if both M.2 are under Ark's specifications, they should work. It's always important to check the distribution of the ports and bandwidth with the motherboard manufacturer (in case they included any limitation or modification) as we don't know which one connects directly to the CPU.
  3. Intel creates the chipsets, and the OEMs can customize them as they intend the PC to work. Because of that, it's better to request this information directly from the OEM.

If you have any other questions please let us know.


Regards, 

David G 

Intel Customer Support Technician 


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David_G_Intel
Moderator
3,526 Views

Were you able to check the previous post?  

Let us know if you still need assistance.    


Best regards,  

David G.  

Intel Customer Support Technician  


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David_G_Intel
Moderator
3,503 Views

We have not heard back from you, so we will close this thread. If you need any additional information, please submit a new question as this thread will no longer be monitored. 


Best regards,  

David G. 

Intel Customer Support Technician  


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