If I use a GB GTX 650 Ti Boost on a board that has 2 PCI-Ex 16x slots, but only supports CrossFire (GB P35-DS4 & EP45-DS5), can I use an old GB 9800GTOC as a dedicated card for PhysX/CUDA in the 2nd slot or would it blow up the computer?
it won't blow up the board but the 9800 would actually slow the gtx650 down especially at games that doesn't use physx. You'd lose more than you gain for extra heat and wasting extra power. You need at least a gtx550 level card for physx
The 9800 would take PhysX processing off ya 650 Ti and thereby increase fps .... not sure how it would work on ya MoBo tho. You can see how an 8800 helped did by googling "Firingsquad Batman PhysX" and seeing the article they did with an 8800 (site is down atm)
it won't blow up the board but the 9800 would actually slow the gtx650 down especially at games that doesn't use physx.
Hm why would it slow the other card down?
It should be the exact opposite (it's also what the others suggest).
Either way I can remove it any time... I was just wondering if it can work at all.
I would think a 9800GT would pair nicely with a entry/mid-level card like the 650 Ti Boost. What PhysX games do you play?
Well the games I've played so far were Mafia II and Batman Arkham Asylum, I think the Crysis series also have PhysX? 9800GT actually andled all these very well in 1980*1080 with PhysX fully enabled, but I still guess some effects were being left out. I mean, for Mafia II they recommended a monster of a card back in the day AND a separate one for PhysX.
I want to upgrade graphics since I upgraded my display to 2560*1440 and the PhysX thing would be a nice extra, maybe.
I'm using Accelero with a silent 12cm fan on a 9800GT so no worries about heat/noise.
A dedicated PhysX card will never slow down your system when not playing PhysX games. It doesn't do anything until told by the system to process PhysX effects.
That's why it's important to make sure you play PhysX games and know what games actually feature GPU-accelerated PhysX. The Crysis series does not use PhysX, but Mafia II and Batman: Arkham do. Here's a list: http://physxinfo.com/
The 9800GT is not going to be the best dedicated PhysX card. There should be a benefit. It likely won't slow down performance, but that would need to be tested and verified. Great that you are willing to experiment and try it out to see.
Key to PhysX performance is the number of CUDA cores and core clock speed. Of course, the GTX 650 Ti Boost is a faster card than a 5870 by about 30% (this is a Hybrid PhysX review), so factor that in. Based on the chart below and the specs of the cards, I would expect the 9800GT to be close to the GTX 250 in PhysX performance. It's good that the 9800GT is overclocked.
GTX 260 has 192 CUDA cores and 576 MHz
GTS 250 has 128 CUDA cores and 738 MHz
9600 GT has 64 CUDA cores and 650 MHz
9800 GT has 112 CUDA cores and 600 MHz