Question about SLI or Xfire

[Jetster]

Whats the rule or ability of said chipset Z68 to have 2 X PCI-E at X16 on both. I notice some boards that have three PCI-E slots have two at X16 but most board with 2 PCI-E are at X16 and X8. ?

AMD has them?

 

[Norton]

Whats the rule or ability of said chipset Z68 to have 2 X PCI-E at X16 on both. I notice some boards that have three PCI-E slots have two at X16 but most board with 2 PCI-E are at X16 and X8. ?

AMD has them?

PCIE lanes are supplied by the MB chipset and/or CPU- this sets the max available for the mobo manufacturer.

AMD Examples (#'s may not be completely accurate- check Wikipedia for the chipset as it's easy to compare)

790X/GX chipset- 22 lanes... X8/X8 (16 total w 6 for other PCIE slots, etc)
790FX chipset- 42 lanes... X16/X16/X8 (40 total w 2 for other PCIE slots, etc)

That's a rough example- not sure what PCIE lanes are available per chipset for Intel stuff

 

[Inceptor]

From what I recall, Z68, like P67 only has 16 PCI-E lanes natively provided.
Some Z68 boards like the Evga Z68 FTW for example, have an additional 16 lanes provided by an nforce controller.
But basically it's 16, so with one graphics card, you're OK for pcie x16, but with 2, in SLI or Xfire, both slots drop to x8 (x8 + x8 = 16).

On AMD boards, like the 990FX for example, there are 40 PCI-E lanes, those boards usually have two slots at x16 that each operate at x16 in SLI or Xfire.

 

[Norton]

Descriptions of PCIE lanes for AMD and Intel can be found here:

http://en.wikipedia.org/wiki/AMD_800_chipset_series#890FX

700 and 900 series chipsets are similar

http://en.wikipedia.org/wiki/Z68#5.2F6_Series_chipsets

Looks like Z68 has 8 lanes in the chipset and SB CPU's have 16 lanes within the CPU= total 24 lanes?