[Foxdog175]

Is the sole purpose for multiple video cards the fact that you can run more than 2 displays? I have an 8800GT coming and I happen to have a Radeon 9800 Pro sitting around. Could I throw that in for a 3rd display? If not for extra displays, what do multiple video cards actually do? They can't work together, can they?

[mduell]

Yes, it's for multiple monitors only. OS X does not support SLI or Crossfire to combine the processing power of multiple cards for a single screen.

[Foxdog175]

Would it be beneficial to use a Radeon 9800 Pro to power a 17" apple display while the 8800 powers a 30" apple display? Would that give the 8800 a little breathing room? What confuses me is what video card gets used as the workhorse.

edit: I realize that the 8800 could power them both without a hitch, but since I have the extra card, I'm thinking why not. Thoughts?

[Mac Write]

The 9800 is AGP while the Mac Pro uses PCI-e therefore (if I am correct) AGP cards can't work in PCI-e slots.

[mduell]

Originally Posted by Foxdog175 

Would it be beneficial to use a Radeon 9800 Pro to power a 17" apple display while the 8800 powers a 30" apple display? Would that give the 8800 a little breathing room? What confuses me is what video card gets used as the workhorse.

Not really, and you'd end up with poorer performance if/when you do something on the 17" that uses the GPU and very little gain on the 30".

Plus there's that little problem of the AGP 9800Pro not fitting or working in the Mac Pro's PCIe slots.

[Foxdog175]

Ah, k. Thanks for clearing that up.

[Cei]

Most graphics cards can drive two displays each - you only need to add a second card when you want triple or quadruple monitors. Your 8800GT will have a pair of dual-link DVI ports, so can run two 30" displays.