Question About CrossFire And PCI-Ex Slot ...

I was doing some reading on the internet, mostly I read on the review and articles of the HD 2900XT. But I was wondering...Take this motherboard as an example - the ASUS P5K-Deluxe With Wifi-AP.My question relates to the PCI-Ex x16 slots, here is one of the specs from the ASUS site.2 x PCI-E x16 (blue @ x16 mode, black @ x4 or x1 mode) supports CrossFire TechnologyNow if the two are x16, then why is the second one at x4/x1 only? Also if this board was to be set up with 2 HD2900XTs on CrossFire, would that mean the the second card will underperform/not perform at it's peak (since it's on a x4/x1 bus)?I know this stuff with SLi, but not that good with CrossFire.Anyone to shed some light on this?Question About CrossFire And PCI-Ex Slot ...
P965 or P35 board, huh?The P965/35 chipset only supports a maximum of 16 PCI-E lanes to one slot only. To add in CrossFire support, motherboard makers either have to:
- Insert a 'crosslink chip' which physically breaks the the signal into two 8 PCI-E lanes (ASUS is bringing out a motherboard with this soon). This is very expensive and complicated, as the motherboard maker has to change the circuitry of the board and the chipset properties.
- Or provide extra PCI-E lanes through the southbridge's (ICH) PCI express channels to the northbridge (MCH e.g. the P35 chipset). This method is much more cost effective, but severely degrades performance. Not because there's only 4 lanes, but because the PCI-E signal has to travel through the southbridge to the northbridge (adds a lot of latency).CrossFire will work, but as you can expect, you'll lose roughy 25-50% of performance compared to running CrossFire on a 975X/CFX3200 chipset. But, before you rush out for a 975X board now, Intel will be bring out a X38 chipset for PC enthusiasts. The X38 chipset supports 'true' x16 + x16 CrossFire, Penryn support, DDR2/3 support, 'capless' overclocking, an improved memory and I/O controller and most of the boards will feature improved voltage delivery. If you're looking at CrossFire, wait for X38.