So in other words i don't need to get it if i will only be using SLI cards? i can put 2 nvidia cards on the pro?
Edit:
It seems the Pro3 (and the Pro4) can do 2 AMD videocards in CrossFire (CF).
But they can't do 2 nVidia videocards in SLI.
You need the Extreme4 or Extreme6 motherboards to do SLI.
A bit weird, but that's what I found in different places.
This is a comparison of features, straight from ASRock's website.
http://www.asrock.com/mb/compare.asp?SelectedModel=Z77+Extreme6&SelectedModel=Z77+Extreme4&SelectedModel=Z77+Pro4&SelectedModel=Z77+Pro3
I found this review of a whole bunch of z77 motherboards.
http://forums.whirlpool.net.au/archive/1903688
http://forums.whirlpool.net.au/forum-replies.cfm?t=1903688&p=3#r41
They mention that the Pro3/Pro4 can do CF, but not SLI. The poster warns that CF is only in 4x/4x mode.
Anyway, it seems clear to me now.
Pro3 is great value for your money, but not SLI.
You need a Extreme4 to do SLI. And maybe also better if you wanna do CF.
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My original post. I was confused .....
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PCI-E slots come in 2 flavors. version 2.0 and version 3.0.
Version 2.0 is what we had over the last years. More than fast enough for any videocard today. Version 3.0 is new. The z77 motherboards are amongst the first motherboards to support PCI-E version 3.0.
Then there is the speed of each slot. PCI-E on a motherboard has limited bandwith (= speed) to the CPU.
Therefor not all slots can run at maximum speed. And certainly not at the same time.
For videocards you always have a "16x" speed slot.
Some motherboards have 2 slots. For 2 videocards. If you stick in only 1 videocard, the slot will run at 16x speed.
If you put in 2 videocards, both slots will run at "8x" speeds.
Note, this is still more than enough to drive 2 videocards. PCI-E is really fast, even at half speed.
And version 3.0 is twice as fast at version 2.0. So slots of version 3.0 at 8x speed, runs just as fast as 16x in version 2.
I hope you could follow this so far.
The point is, I had though that the cheap mobos would have only 1 16x PCI-E slot. Like the Pro3.
And if you wanted 2 slots, you needed more expensive cards. Like the Extreme 4.
I just tried to check that.
It seems I was wrong.
The ASRock z77 Pro3 seems to have one 16x version-2 slot, and another 16x version 3 slot !
So if you want to use SLI/CF on the Asus Pro3, that is in fact possible !
I am confused now.
Why would anyone ever want to buy an Extreme 4 motherboard ? And not just the much cheaper Pro3 ??
Within 1 or 2 weeks, I will order my own new PC.
If this is true, I will buy a Pro3 myself.
The specs of the ASRock Z77 Pro3: http://www.asrock.com/mb/overview.asp?Model=Z77%20Pro3
And the ASRock Z77 Extrem4: http://www.asrock.com/mb/overview.asp?Model=Z77%20Extreme4
From the pictures, it looks like the the Extreme4 might have 4 slots for videocards, and the Pro3 only 2 slots.
If someone knows for sure, please enlighten us.

TIA.