CUDA Question

[LokutusofBorg]

If I want to buy a 4870 to drive my display(s) can I buy a really cheap nVidia card (like a 9400GT or something) and have CUDA-enabled apps make use of it? Will it affect the primary video card, by like bumping the x16 down to x8 or whatever? (MSI X58 Pro, or UD3P/DS3L)

Thanks.

 

[aka1nas]

It should be fine as long as you aren't running Vista. Cuda performance (just like PhysX) is often (but not always) very dependent on the number of shaders on the GPU.

 

[LokutusofBorg]

Hmm... I'll be running Vista on my new build.

 

[ViRGE]

It should work, but you're going to need to wait for Windows 7. Vista can't handle two sets of WDDM drivers simultaneously.

As for how it will affect the primary video card, it depends on the board you use. The X58 boards all have 2 (or more) full bandwidth x16 slots so you should be fine. The UD3P/DS3L are based on the P45 chipset, which does not have enough bandwidth for 2 x16 slots. I'm assuming you'd go down to x8/x8 or something like that.

 

[Keysplayr]

Originally posted by: ViRGE
It should work, but you're going to need to wait for Windows 7. Vista can't handle two sets of WDDM drivers simultaneously.

As for how it will affect the primary video card, it depends on the board you use. The X58 boards all have 2 (or more) full bandwidth x16 slots so you should be fine. The UD3P/DS3L are based on the P45 chipset, which does not have enough bandwidth for 2 x16 slots. I'm assuming you'd go down to x8/x8 or something like that.

Although I haven't seen any information that shows diminished CUDA performance on anything less than x16 PCI-e. Have you? If so, please link it up. Same goes for graphics cards. Nothing very definitive showing diminished graphics performance on say an x8 PCI-e connection over a x16. Many say even the x8 connection isn't close to saturated even with todays monster GPU's. If you have any info contrary to this and is definitive, please let us know.

 

[Zap]

Originally posted by: LokutusofBorg
If I want to buy a 4870 to drive my display(s) can I buy a really cheap nVidia card (like a 9400GT or something) and have CUDA-enabled apps make use of it?

Whether or not you can get it working, the 9400 GT is not a great choice for CUDA. The reason is that it only has 16 shader processors. Another $20-30 would DOUBLE that to 32 on a 9500 GT, and another $20-30 would DOUBLE it again on a 9600 GT to 64. Most of the terrific performance gains you read about that CUDA enables were probably done on a GTX 200 series card, which starts with 192 shader processors. I think if you start that low, you'd be setting yourself up for a disappointment. If you really, REALLY want CUDA support, the best thing to do would probably to get a GTS 250 (128 processors) or a current generation GTX 260 (216 processors). You're looking at a bit below the 4870 in price for the former, and a bit above for the latter. Besides getting much better CUDA performance, you wouldn't have to deal with Vista driver issues, you wouldn't have to own a motherboard with multiple PCI Express slots capable of handling video cards and you wouldn't have to own a power supply capable of handling two graphics cards.

Think on this before you buy. There's nothing CUDA can do that your CPU cannot. However, some things CUDA can do faster (maybe not better, just faster). If you feel it is worth having CUDA, skip the ATI card. If you feel it is not, get what you would rather have.

 

[LokutusofBorg]

Great advice, Zap, thanks.