Can the 4870 run happily at 4x PCI-e?

[Peter Trend]

Hi,

I'm considering getting a second card for my ASUS board (see sig for specs).
The board has 3 full-size slots: 1 at 16x, one at 8x and one at 4x. If you use the 8x slot then the 16x runs at 8x instead.

I have one 4870, and I am considering getting either another 4870 or a 4870x2. I plan to eventually get both. The plan is to install like this:

16x/8x (top slot) - 4870x2
8x (middle slot) - 4870
4x (bottom slot) - 4870

If I run them like this, is it likely to work well?

 

[Quiksilver]

I don't know the answer to your question, but what exactly are you doing that would benefit from you doing this?

 

[error8]

A 4870 X2 needs the full bandwidth of your PCI express 2.0 slot. It's not going to use it all, but I guess it needs more then 8x is able to provide. A 4870 would probably have no performance loss on an 8x slot, but it will be bottlenecked on a 4x.

 

[Peter Trend]

what exactly are you doing that would benefit from you doing this?

Folding proteins using GPGPU, gaming and messing about (who knows what else I'll use them for though, I like experimenting).

A 4870 X2 needs the full bandwidth of your PCI express 2.0 slot. It's not going to use it all, but I guess it needs more then 8x is able to provide. A 4870 would probably have no performance loss on an 8x slot, but it will be bottlenecked on a 4x.

Okay, so to run them at full speed I can only use either one 4870x2 or two 4870s? Makes sense.
I'm still expecting to see a performance gain using 3 GPUs instead of 2, the real question Im asking myself is whether to buy a 4870 now or a 4870x2. Or indeed wait until RV790?

 

[Peter Trend]

And then of course theres the question of whether the 4900 series will actually be crossfire-x compatible with the 4870!? And what price range they will come into.

 

[OCGuy]

Why not spend the money on a mobo with 2X 16x slots and just do Crossfire-X?

 

[Peter Trend]

Mainly because its a new motherboard and I really like it so far. And because a mobo swap needs a reinstall of windoze, but I don't have an awful lot of spare time to do that again right now.
I doubt I will change mobo until I move to intel in about a year, I just want to get the best out of the one I currently have. Its not all about cost either, a lot of it is about hassle.

Thanks for your opinion though Im probably just going to get another 4870 and forget about the 4870x2 for now

 

[VirtualLarry]

The ATI cards (currently) don't produce as much PPD as the NV cards. Something to consider.

Additionally, I think that your gaming might be crippled by using 4x slots with a 4870 in a CF config. Don't CF cards scale down to the speed of the slowest one?

 

[Denithor]

Originally posted by: VirtualLarry
The ATI cards (currently) don't produce as much PPD as the NV cards. Something to consider.

Additionally, I think that your gaming might be crippled by using 4x slots with a 4870 in a CF config. Don't CF cards scale down to the speed of the slowest one?

Exactly. nVidia cards crank out about 2x the ppd from equivalent cards. The G92-based cards give 4-5k ppd and the G200 cards give 7-9k ppd. Compared to the 4870 which will hit around 3-4k ppd.