Phil_Boggild

I'm going to be upgrading to a 1920x1200 monitor soon, and with it, a new graphics configuration.

Having heard about the 8x/8x PCIe issue with P45 boards like mine, I totally wrote off the idea of Crossfire right from the start, and was leaning towards getting a GTX 295.

However, lots of people are telling me to go with the cheaper, faster alternative of running two 4890's instead.

My question is, with the two PCIe lanes at 8x instead of 16x, is it really going to be worth it? I'm constantly finding wildly conflicting opinions on the matter, and I don't want to buy two new cards if I'm not going to be able to get as much out of them as I can. If the impact it would have is negligible then I obviously don't mind.

Just about everyone who's against the idea of Crossfire on a P45 sites this test as an example:-

http://www.tweaktown.com/articles/14...ce/index7.html

Many other tests show differing results. People seem to be completely divided as to whether or not there's a huge bottleneck, some citing the fact that PCIe 2.0 has enough bandwidth, others saying that it would be a waste.

I'm really confused.

corky dorkelson

I don't even know what to think on the matter any more. But mostly what I hear is that the x8 is going to rob you of about 5% vs a x16 configuration. That is peanuts, really.

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Phil_Boggild

http://www.legionhardware.com/document.php?id=761&p=8

Yes, this test would tend to agree with you. They found only a 5% difference, and that's nothing really. At the resolution I would be playing at - 1920 x 1200 - it amounted in most cases to no more than 1-2 fps.

The more input I can get on this, the better.

TEntel

Stock 4890s will not be bottlenecked on x8 lanes.


If you overclock the memory though, that'll be pushing it.


http://www.overclock.net/ati/538973-...vs-8x-pci.html

Check out post #11 by rico2001

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tipsycoma

I'm in the same position as you are. I've been researching up the arse trying to figure out whether to go P45 or X48. or 790GX rather than 790FX. The difference is that the PCIe lanes are full bandwidth in the newer chipsets. I saw that TweakTown review a while back, and it seems pretty straightforward. Even at PCIe 2.0, x8 bandwidth will hinder the performance of better cards. PCIe 2.0 is supposed to double the bandwidth, so reallyx8 on 2.0 is equivalent to PCIe 1.0 x16. And PCIe 1.0 at x16 has a bottleneck in performance. I know this because I had a P35 board that was PCIe 1.0, and my 4850 ran 5-10 FPS lower in Crysis. Now in CF 4890's if you had something equivalent to PCIe 1.0 x16 you'd feel even more of a bottleneck. Right now, go with a more advanced chipsets. Those old P45's aren't worth the saving of 50 bucks for, especially if you have two 4890s. That's my opinion, and what I'm going to do.

almighty15

It's gonna cripple them, just sell up and get a 4870x2

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TEntel

There has to be something else going on. No way is a 4850 going to be bottlenecked by a PCI-E x8 slot.

Maybe it has something to do with PCI-E 1.0 vs PCI-E 1.1

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tipsycoma

Apparently tweaktown proved that it did, in Crossfire. I don't know how trustworthy they are but regardless, he's simply better off with a x16 x16 board, especially with 4890s/

Phil_Boggild

See what I mean? Literally completely opposing views.

While there are quite a few tests that show the difference to be only 5-10%, none of those tests are done with anything above a 4850. I really don't know if taking a leap of faith is a good idea, so I'm just going to have to keep looking to see what I can turn up.

rico2001

see here:
http://www.overclock.net/6858896-post2214.html

That tweaktown review is garbage.

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My reviews:
4870, 4870 Tri-fire, 4850 X2 Quad-fire, 4850 X2 vs. 4870 X2,
4850 X2 + 4870 Tri-fire, 4850 X2 + 4870 X2 Quad-fire, 4850 + 4870 Crossfire,
(NEW) 4890 vs. 4850 X2

Steam nick: rico2001

"The ability to learn faster than your competitors may be only sustainable competitive advantage." ~Arie de Geus