PCIe slots and graphic cards.

[Soard666]

Hi guys! I'm new to this forum. And I have a couple of questions if I may please kindly trouble you with?

I'd like to please ask you for an explanation about PCIes concerning graphics cards in particular especially focusing on multiple GPUs and multiple graphics cards.

My problem is that though I do have 3 PCIe 2.0 slots on each of my two motherboards, I don't think I could use 3 ATI cards in crossfire mode with all cards running at full power!

I have two x58 based boards. One is the ASUS Rampage II Extreme, and one is the ASUS Sabertooth x58.

On the Rampage II model, the manual tells me that if I use 3 way graphics (SLI or Crossfire) the PCIe speeds would be x16, x8, x8. Note: PCIeX1-1 slot is occupied by the bundled audio card!

On the Sabertooth model, the manual tells me that that it can support only 2 way SLI and 3 way Crossfire (Quad-GPU if used in 2 way crossfire with dual GPU graphics cards). The PCIe speeds using 3 way crossfire would be: 16x, 16x, 4x. (Last PCIe x16 would run at x1 if PCIeX1-2 slot was occupied). And then it tells me that if I were to use 3 way crossfire, it is recommended that I occupy PCIex1-1 slot with an x1 card for best performance.

I donno about you sir, but I'm so confused, if I were to cat scan my head, my brains would be showing as jello!!!

I have some questions about all this... like:

1- Why don't all PCIe's run at X16?

2- Why does the Rampage II run its PCIe's in 3 way graphics card mode at: x16, x8, x8 when the Sabertooth runs them at: x16, x16, x4?

3- If I follow the instructions of the manual on the Sabertooth and install an x1 card in PCIex1-1 slot, wouldn't it drop the speed of PCIex16-3 from x4 to x1?! How would that be recommended for better performance?! Isn't x4 faster than x1?!

4- This whole questionnaire is just for me to answer the dolting question: should I get another HD 5770 and run 3 way crossfire? Or should I leave it at just 2 way? Would my graphics performance increase, even if by a margin using 3 way on this card? Or will it actually drop the total performance?

Could I please kindly trouble you with answers to these questions so I may regain my sanity?

Thank you so much!

Best regards!

Soard

 

[tinytomlogan]

The Northbidge only has a certain amount of pcie lanes available.

Some of the lanes are on the chipset (most of them) but with some motherboards they can add extra chips (lucid, plx ect) in to allow more lanes. How the PCIE lanes are shared can be set how ever the manu wants via the bios ect.

Just something you need to consider when choosing a new mbo.

GPU wise Id actually look at new cards as multi gpu set ups in more than dual mode just runs into so many problems tbh.

You need to spend your money on a newer GPU rather than just adding more old ones

 

[Soard666]

The Northbidge only has a certain amount of pcie lanes available.

Some of the lanes are on the chipset (most of them) but with some motherboards they can add extra chips (lucid, plx ect) in to allow more lanes. How the PCIE lanes are shared can be set how ever the manu wants via the bios ect.

Just something you need to consider when choosing a new mbo.

GPU wise Id actually look at new cards as multi gpu set ups in more than dual mode just runs into so many problems tbh.

You need to spend your money on a newer GPU rather than just adding more old ones

That's it?

After all this speech I made?!

Any way... thanks, though you did not fully answer my question, you did pave the way for me to better search what I was looking for. Thanks to you I learned from research that x58 chips have a total of 40 PCIe lanes, of which 36 are reserved for PCIe2. That is what I was looking for! Now I better understand how those lanes are divided.

However, I still don't understand the Sabertooth x58's advise of occupying the PCIe x1-1 lane so that the 3rd PCIe x16 slot, which already runs on x4, to run better, when doing so will actually drop the speed of the last PCIe x16 slot from x4 to x1! Does occupying a certain number and order of slots create some kind of.... more efficient logical circuit or something? I'm stumped on this part!

Would you like to add something to that please?

Thanks!