5850, 8x pci-e vs 16x

[drunkenmaster]

Wanted to ask if anyone else could knock their pci-e slot down to 8x and see if something like vantage or a game benchmark gives significantly lower scores.

I got a 5850 yesterday but my vantage numbers(mostly using to look for max mem speeds) weren't where they should be. Further looking around and I noticed the slot was running 8x, even though it was 16x with the previous 4890 and 16x selected in bios, much messing around and I couldn't get it.

With 835/1250 set in gpu clock tool, it was only getting around 12.5k gpu score in performance mode.

Finally switched it to the next 16x slot on my mobo, its finally working at 16x and my score jumped from 12.5k to around 15.2k. The two game tests were getting around 40/32fps, and now get 44/43fps.

Wanting to know if thats solely down to the pci-e being at 8x, or if its the slot is also smegged, and so theres another issue.

If its just 8x pci-e, it would mean these cards REALLY need a 16x slot, which means, the 2x8pci-e's on the new intel boards is going to kill performance significantly for crossfire.

 

[RavenXXX2]

You running a PCI-E 2.0 mobo?

 

[HeX]

Was that an 8x PCI-E 2.0 slot? or was it just running 8x in 1.1?

 

[Greebo]

I suspect it is more than the 8x speed.

Reason being is that this review here with two high end cards only shows a 2-3% drop going to 8x speed.

http://www.tomshardware.co.uk/geforce-gtx-sli,review-31577.html


8 x speed should be more then enough bandwidth for a single 5850

 

[drunkenmaster]

pci-e 2.0, was 8x, now 16x with a , well, 25% bump in performance doing so.

But like I said, if someone can confirm or disprove the results by changing their slot(if you have the bios option) to 8x we can see if bandwidth is a far bigger issue.

But like I said, its that, or my first slot is dodgey, meaning maybe mobo on the way out or some other issue, which is more than possible as I couldn't get the card to run at 16x under any circumstances at all in the first slot. DFI 790fx-b board, has 3 slots, one 16x which should always be 16x unless I change it manually, the other 2 slots run either 16x as one(which I'm doing right now) or 8x/8x.

Personally I wouldn't have, and still don't quite expect it should make that much difference, so I still think its probably an issue with my board, which I could do with other results to confirm that. But its also possible 8x is simply no where near enough for a 58XX card.

 

[Greebo]

I won't get my card until tomorrow so can't check until then.

Just a thought in the meantime, why not manual change the slot it's in to 8x or tape of the pins and try it on 8x in your working 16x slot.

If there is no drop in performance (eg same as 16x) then you know your main slot is fubar.

EDIT: And I finally found the article I was looking for earlier:

http://techpowerup.com/reviews/AMD/HD_5870_PCI-Express_Scaling/

As you can see, a 5870 only drops 1 to 2% depending on res so only 1-2fps in the games max.

 

[Jakus]

It would not make that much difference if it was an AGP slot!, You have other issues there, Mobo/bios

You know those Cards will throttle if You over push the memory ?