In our Core 2 Duo motherboard roundup in Hardware.Info Magazine #4/2006, the ASUS P5W DH came out as the clear winner and we claimed that it was the ultimate Core 2 Duo motherboard currently available. It seems that even perfection can be improved on and that's what ASUS have done with the P5W64 professional. This motherboard is the Workstation model of the ASUS P5W DH and offers space for up to no less than four video cards!
Looking at the motherboard the first thing you'll notice is a quartet of PCI-Express x16 slots lined up one after the other. ASUS have made this possible by adding an IDT 89HA0324 PCI-Express switch to the motherboard. This chip basically regulates the shared usage of eight PCI-Express lanes between two slots. The two slots connected through the IDT-chip basically take turns in using the eight lanes. The actual speed of both slots is comparable to PCI-Express x4.
How does the allocation of the PCI-Express lanes actually take place? You can select one of two options in the BIOS. Selecting option 1 causes the 16 lanes of the Intel 975X to be divided into 2 x 8 lanes. The first eight lanes are then allocated to slot 1, the other 8 are allocated to the IDT switch which in turn allocates the lanes to slots 2 and 4. The third slot is controlled by the ICH7R south bridge and has to make do with four PCI-Express lanes. In essence what this comes down to is a configuration of x8/ x8/ x4/ x8 lanes.
When selecting the second option the 16 lanes of the north bridge are not divided and go directly to the top slot. In this mode the IDT switch doesn't get designated any PCI-Express lanes to it, hence in this mode slots 2 and 4 are basically idle. Selecting option two sets the configuration to x16/ x0/ x4/ x0.
Allocation of the PCI-Express lanes for the four slots on the ASUS P5W64 WS
The four PCI-Express slots are not just suited to video cards. In theory you could insert a load of RAID-controllers, video-editing cards or any other PCI-Express cards that you wish. The Motherboard is clearly meant to be used in a workstation and luckily more and more professional PCI-Express cards are being released on a regular basis.
For anyone who's asking themselves if there is such a thing as Quad-Crossfire, the answer would regrettably have to be no. Theoretically the P5W64 professional should be capable of supporting such a set-up, but as of yet there are no ATI drivers that support the use of four cards. ATI have released information that it is possible to have two video cards running in a Crossfire set-up with a third card handling only the physics calculations. A beautiful thought to contemplate about but not an implementation that we would see in the near future.