Tom's Hardware > Forum > Graphic & Displays > Graphics Cards > 8x vs 16x issue
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fchowd0696   07-04-2008 at 02:09:29 AM

I have two hd4850s in my hand....

I have a p5q deluxe, thus if I want to run this in crossfire I would have to sacrifice 16x speeds. With some games not taking advantage of crossfire I would assume those games in crossfire would actually be worse in performance than a single 4850. My question is how much of a hit would I take with games that do not take advantage of crossfire.

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FrozenGpu   07-04-2008 at 02:11:27 AM
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what resolution are you playing at first?

I know somebody posted the links to the sites that have reviewed this issue b4, i thought it was like less than 10-5%

Not a huge deal if you think about it....

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fchowd0696   07-04-2008 at 02:22:31 AM
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FrozenGpu wrote :

what resolution are you playing at first?

I know somebody posted the links to the sites that have reviewed this issue b4, i thought it was like less than 10-5%

Not a huge deal if you think about it....


its a 22 inch samsung native rez at 1680 x 1050.

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FrozenGpu   07-04-2008 at 02:37:46 AM
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fchowd0696 wrote :

its a 22 inch samsung native rez at 1680 x 1050.



if u search this forum for like P45 or something similar u will find those charts that show what i was talking about, unless of course u play FSX, and only really that then the frame rate loss is pretty small...

To be brutally honest, I wouldn't be bothered by it too much, b/c it doesn't have the impact say a 4x slot would have, which is quite noticeable, this is much less noticeable, so go ahead!

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pauldh   07-04-2008 at 06:21:23 AM
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I think it's almost a total non- issue. Crossfire HD4850 would be even better, but look how 8800GTS 512MB SLI performs the same on a 750i SLI (8x/8x) as on 780i SLI (16x/16x):
http://www.firingsquad.com/hardwar [...] page11.asp

I researched this when buying a mobo for 8800GT SLI plans and found little to no difference in the reviews I could find. So I decided to save money and buy a 650i vs 680i at the time. Eventually this should change, but not sure if we are even really there yet with GTX 280 SLI in current games.

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zipz0p   07-04-2008 at 06:41:22 AM
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If you've already got the cards and the board, don't sweat it. It looks like at worst it'll give you a 10%ish decrease in performance (compared to dual x16 links), but probably not for most instances. It shouldn't really perform worse than a single 4850 almost ever.

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pauldh   07-04-2008 at 06:43:23 AM
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dirtmountain wrote :

Tweaktowns article on this
http://www.tweaktown.com/articles/ [...] index.html


I have a hard time believing there is such a difference (edit: just from 8x vs 16x) with crossfire 4850's when SLI shows zero difference at 19x12 4xaa even. Very strange yet interesting results I would like to explore this or see it explored in depth.


Here is the techspot 650i/680i comparison with 8800GTX SLI:
http://www.techspot.com/review/45- [...] page4.html


Message edited by pauldh on 07-04-2008 at 06:44:28 AM
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pauldh   07-04-2008 at 06:56:07 AM
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http://www.anandtech.com/video/sho [...] =3341&p=20

Check out COD4. I find it interesting just how good crossfire HD4870 did on the X48 vs a single 4870 on 790i. > 100% scaling shows how good X48 is in comparison.

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dirtmountain   07-04-2008 at 06:57:26 AM
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I agree with you Pauldh, it seemed a much bigger hit then it should take. I just can't find much more info on it though. My bet is that is will a very small effect.

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pauldh   07-04-2008 at 07:01:46 AM
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Only other P45 vs X48 crossfire I have seen was HD3870's and low res..... nothing that could challenge techspots findings.


Imagine if it proves to be an accurate picture!!! If it is true, forget 8x/8x crossfire HD48x0 series.

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JDocs   07-04-2008 at 07:32:33 AM
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Also the P45 boards use second gen PCI-e which, in theory, have twice the bandwidth so you'll still, again in theory, be getting x16 first gen speeds on each port. Since the 4850 can't fully saturate a first gen PCI-e X16 slot I think it won't effect your performance.

 

Edit: At resolutions you can actually play at the 4850 can't saturate a first gen x16 port.

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Message edited by JDocs on 07-04-2008 at 07:40:01 AM
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FrozenGpu   07-04-2008 at 11:42:56 AM
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JDocs wrote :

Also the P45 boards use second gen PCI-e which, in theory, have twice the bandwidth so you'll still, again in theory, be getting x16 first gen speeds on each port. Since the 4850 can't fully saturate a first gen PCI-e X16 slot I think it won't effect your performance.

Edit: At resolutions you can actually play at the 4850 can't saturate a first gen x16 port.



See that's the thing, it really doesn't saturate it as much as PCI-Express 1.0 did, well running 8x/8x mode as opposed to 16x/16x.

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