Closer Look: RADEON XPRESS 200 CrossFire Edition Mainboard
A mainboard based on a RADEON XPRESS 200 CrossFire Edition chipset is needed to build a CrossFire platform and we are grateful to ATI Technologies for their giving us not only two RADEON X850 XT graphics cards but also an appropriate mainboard to perform our tests on. We traditionally use an AMD Athlon 64 4000+ processor in our testbed, so the mainboard we received was based on a RD480+SB450 chipset. The mainboard looks most impressive with its red slots and black lacquered PCB:
Ours was an engineering sample, with traces of colophony, numerous engineering connectors and jumpers and a not very convenient layout – the mainboard offers no expansion opportunities other than two PCI Express x16 and two PCI slots. The PCI slots are most inappropriately placed, too. The bottom PCI Express x16 slot is the Master, so the first PCI slot gets automatically blocked by the dual-slot cooling system of the RADEON X850 XT CrossFire Edition. It is the stranger then to see an abundance of free space under the second PCI slot – this part of the PCB is empty save for the diagnostic LED indicator with its Xilinx chip and an ATI logo! We think the PCI slots could be placed lower. It wouldn’t make the wiring of the PCB much more complex, but would make both slots available for use.
The PCI Express x16 are not configured on the software level as you might think looking at the empty space between them. The mode selector here is a special textolite terminator card which is installed into the top PCI Express x16 slot if there’s only one graphics card in the system.
If you do not use the selector, the bottom slot will work as PCI Express x8, causing a certain performance hit. Moreover, you have to activate the appropriate BIOS option after you’ve installed two graphics cards. We do not know if such a selector will be used in off-the-shelf mainboards. We think that at least some mainboard makers will offer software selection of the PCI Express modes since the selector is not convenient. It is not fixed in the slot and can be broken or lost, making it impossible to use the Master slot in the PCI Express x16 mode.