X8/x8 bottleneck?

[HostileDonut]

So, normally x8 is enough for a crossfire setup, but then I heard that the hd4850 uses a lot of bandwidth and that it is bottlenecked by the x8 PCI-E 2.0 slot. If I ran two hd4850s CF would it be bottlenecked by 8x/8x?

 

[iam2thecrowe]

ive never heard anything specific to that card, but generally the loss wont be more than 5% http://www.tweaktown.com/articles/1472/intel_p45_vs_x48_crossfire_performance/index.html maybe check exactly what motherboard you have, that may be a factor. the 2 boards in the link 1 has 8x 8x the other has 16x 16x. weather or not all 8x boards perform like this i dont know.
more food for thought http://www.overclockers.com/forums/showthread.php?t=629631 and more http://www.google.com.au/search?sourceid=chrome&ie=UTF-8&q=4850+crossfire+8x

 

[militant atheist]

They generally don't cause much problems till you get to the real high-performance cards (5970's whatnot). http://www.hardocp.com/article/2010/08/23/gtx_480_sli_pcie_bandwidth_perf_x16x16_vs_x8x8/3

 

[Annisman]

An article I read (too lazy to find it) tested the highest end cards on the market in different PCIEx speeds. It pretty much concluded that 8x/8x will only be a few percentage of a decrease in performance, but that is on the best video cards, which an hd 4850 is not.

Also, I will add, that an 8x/16x array shows almost no loss in performance (that is what I am running)

So, youre good to go.

 

[militant atheist]

An article I read (too lazy to find it) tested the highest end cards on the market in different PCIEx speeds. It pretty much concluded that 8x/8x will only be a few percentage of a decrease in performance, but that is on the best video cards, which an hd 4850 is not.

Also, I will add, that an 8x/16x array shows almost no loss in performance (that is what I am running)

So, youre good to go.

I read the same article once upon a time, and I couldn't find it when I searched for this.

 

[mactronix]

As the rest are saying its not a real issue. yes it will be slower by about 3-5% would be my guess but nothing you would notice. Put it this way, if you ran your cards on a X8 and then a X16 capable board you wouldn't be able to tell which one you were using.

Mactronix

 

[megamanx00]

There's a small performance penalty going with 8x/8x instead of 16x/16x. How much depends on the cards used and the game. For some games there is no discernible penalty even with two high end cards. On others it may be noticeable depending on the cards and settings used. For two 4850s though the difference is pretty small. Legion Hardware does a few articles on SLI and Crossfire scaling so you may want to check out an older one they have about 4850 CF scaling if you're really that interested.

 

[g8orboy11]

Anyone know how much a 4x/16x would bottleneck a card?

 

[HostileDonut]

Thanks for all the replys guys! Now I don't need to buy an MSI 790FX motherboard!

 

[HostileDonut]

A 6990 isn't even bottlenecked by an X8 slot. Whoever told you that didn't have a clue

WOAH! So, the x8 slot is really strong. Someone linked a thread that said it should go through the northbridge and not the SB I think, so how do I figure which one it goes through?

 

[HostileDonut]

SWEET!

 

[g8orboy11]

Kinda answered my question too, so thanks.

 

[HostileDonut]

Anyone know how much a 4x/16x would bottleneck a card?

16x 4x is a bad SLi or CFx setup. You want to avoid that. Sorry.

 

[HostileDonut]

It won't be TOO bad

Last article I read it was about a 25% decrease in performance.

 

[iam2thecrowe]

http://www.tweaktown.com/articles/1472/intel_p45_vs_x48_crossfire_performance/index8.html if you did read the link i posted you will see ther can be a significant performance loss, this showing between p45 and x48 chipsets. probably will be ok on an amd based chipset though

 

[HostileDonut]

Okay, thanks! I am using AMD.