Mobos PCIe slots - 16x or 8x / 8x - HALP!

[Tsuchi]

Hey all,

So I'm looking at putting another computer together, and for the CPU I had my eye on the I7 860. The problem with this seems that the appropriate mother boards have an odd PCIe issue. The options are to one run card at 16x or two at 8x / 8x. What does that mean for me? Does that mean that each card is at only half capacity, rendering SLI/Crossfire useless?

Any insight appreciated!

Thanks,
Tsuchi

 

[Zargon]

isn't that normal?

 

[Tsuchi]

I have no idea Every time I come back to build something I see something different. Is running 8x / 8x normal, or is 16x / 16x normal? Or is 16x / 16x not even possible for SLI? I dunno how that all works.

 

[lopri]

If you have two video cards in an i7-860 system, then they will be @x8/x8 and that is normal. If you have one video card and some other PCIe card (such as a RAID or a Network card) in the PCIe slot rooted in the CPU, then your video card will operate @x8 bandwidth and that is normal. If you have one video card and install it in the 2nd PCIe slot (also rooted in the CPU) then you will get x8 bandwidth and that is normal as well.

On P55 platform, the CPU provides total x16 PCIe lanes (faster) and the PCH provides x8 PCIe lanes (slower). Out of the x8 lanes available through PCH, some of them are used for network PHY or additional storage controllers, so on most boards you'll see a x4 slot at most.

x16/x16 is not possible with i7-860 but you need not lose sleep over it. x8/x8 is plenty.

http://www.anandtech.com/mb/showdoc.aspx?i=3649

 

[dflynchimp]

PCI-e 1.0 has some motherboard options with 32X (meaning full X16 + X16 for multi-gpu)

This however is equal in bandwidth to PCI-e 2.0 at X8 + X8 since 2.0 doubles the bandwidth over 1.0

In other words, the maximum bandwidth for multi-card setups hasn't changed for a while. The good news is that we aren't at the point where bandwidth is a major limitation. I keep telling people that even my 4870X2 is only seeing a 2% penalty from using a 1.0 X 16 slot (half of 2.0 X16).

If you have the money and the psu to boot, then by all means go dual card.

Bottom line is don't worry about the bandwidth. It won't slow your cards down at all.

 

[Tsuchi]

Thankee much for the input. This is why I love these forums and the contributors. Thats all I needed to know ^_^

Thanks again,
Tsuchi