Max PCI lanes in a cpu

[pcnewbies]

So i was planning to make a new gaming computer. I looked through the cpu chips and the Intel® Core™ i7-4790 Processor (8M Cache, up to 4.00 GHz) has caught my eye. However i am confused when i see the max pci lanes being only 16. Does that mean if i put the chip on a Gigabyte GA-Z97X-Gaming G1 WIFI-BK ATX LGA1150 Motherboard, and place 2 GTX 970 in 2 pcie x16 slots with sli, it will become x8/x8?

 

[Someone Somewhere]

I'm assuming you mean PCIe rather than PCI.

Yes, that board will max out at x8/x8. However, not all boards act in that exact way.

Running at x8/x8 will cause negligible performance loss compared to x16/x16.

 

[MeteorsRaining]

No, since the MoBo uses multiplier chip (PLX chip) which basically uses bridge switches, which enables access to a greater number of lanes. Your SLI config will run at full x16/x16. Good info here:
http://www.tomshardware.com/reviews/graphics-performance-myths-debunked,3739-2.html

PS: As stated earlier, it doesn't have any effect on performance. It just allows a config of more GPUs (like 4 way SLI).

 

[Someone Somewhere]

Oh, oops. Forgot about those pesky chips.

 

[pcnewbies]

Oh cool thanks for the replies 😀

 

[Karsten75]

There are two ways motherboards deal with this. One is to allocate fewer PCIe lanes as you put in more PCIe devices (as you surmised) - the method they do this is usually described in the technical specifications for the motherboard.

The other way on high-end motherboards is to add a PLEX chip that will handle multiplexing of the PSIe lanes - so each slot can have more lanes, and the PLEX chip will miltiplex them together on the PCIe lanes for the CPU (highly simplified).

http://www.gigabyte.com/products/product-page.aspx?pid=4980#sp

Under Expansion Slots you can read how it handles up to three cards in the PCIe slots (hint at three cards, it drops down to PCIe 2.0 standards).

I'm puzzled how it will support 4 cards in SLI, since they don't mention that part and it does not have a PLEX chip as far as I can tell. The price is also indicative that it doesn't have a PLEX chip. Those usually drive the price to >$200.

Edit: I now read where some reviews does say that it has a PLEX chip, so all should be good. MeteorsRaining has all the right info in his post that you already selected as Best.

 

[Marcus52]

This board does NOT have a PLX chip and 2 cards will run at x8 x8.

This isn't really a concern unless you want to get every drop of potential juice out of the graphics cards or want to buy a MB that will support future graphics cards that saturate PCIe 3.0 x16.

Otherwise, you need a socket 1150 with the PLX chip or to go to Socket 2011-v3 (Haswell-E). The latter gives you a choice of CPUs providing 28 or 40 lanes of PCIe 3.0.

 

[Karsten75]

This board does NOT have a PLX chip and 2 cards will run at x8 x8.

.

Well, both Hardwaresecrets and another review I read earlier indicates that this mobo does have a PLEX (or PLX) chip.

Please provide your references for saying it doesn't have one?

Edit: Legitreviews also says it has a PLX chip.