Crossfire & SLI - PCIEX x8 vs x16

[almighty]

Hey guys, I run some tests on another forum between running in x8 and x16 mode to see what effect it had on modern games, It's nothing special but thought some of you might be interested in the results.

Do note that I only have 2Gb of RAM because one of my sticks died.

Because of this frame rates are lower then normal because of a lack of system RAM.

Anyway, results are mixed

Crysis, x16, No texture Packs :

Crysis, x8, No texture Packs :

Those looking close will see that the x8 con fig has a higher minimum frame rate then the x16 con fig, That's because I restarted windows so it had a bit more System RAM free.

Crysis, x16, With Rygels Texture pack :

Crysis, x8, With Rygels Texture pack :

The minimum frame rate took a hit when running in x8 mode, this is due to the texture pack requiring more then 1Gb of VRAM and having to send quite abit of data over the limit x8 connection. Still not as big of a hit as I was expecting.

STALKER : Clear Sky, x16 :

STALKER : Clear Sky, x8 :

I was expecting more of a difference then that. Especially with these 2 titles as they are the most demanding games available at the moment.

Mind you, I do run Clear Sky with a texture pack that I couldn't get to load in the Clear Sky benchmark, Maybe that would of put extra stress on the VRAM and made a difference to the results?

I also wonder if my low resolution has anything to do with it?

So basically if you have enough VRAM to handle the games you play then you should be fine with x8x8 BUT if you play VRAM heavy games then you might see a performance drop.

People with 512mb cards beware.

The GPU is a 4890 and my CPU is a 4.2Ghz Pentium Dual Core E6300

It's not the most accurate or controlled but it gives you an idea.

 

[Davros]

how are you changing your pcie slot to x8 ?

 

[Kaotik]

how are you changing your pcie slot to x8 ?

Yeah, curious about this myself too, taping the pins on the card or some software trickery?

 

[ShaidarHaran]

1280x1024 is hardly a GPU-limited resolution even for Crysis/Stalker. Could you test again with a higher res or are you limited by your monitor?

 

[almighty]

It's easy, take my GPU out of PCIEX slot one and put it in slot number 2

And I'm limited by my monitor

 

[Davros]

ahh, you have one pci-e x16 and one pc-e x8 slot

any compatibility problems with the x8 slot ?
my pc upstairs has a x4 slot (because it also has agp) and apparently some cards dont work with it

 

[ShaidarHaran]

Davros -

I take the OP's comments to mean his 2nd PEG slot is electrically x8, not physically.

 

[Davros]

yes, my x4 slot is x16 physically, x4 electrically

 

[almighty]

4890 worked with no issues at x8

 

[Humus]

I was expecting more of a difference then that.

I wouldn't expect a larger difference normally.

how are you changing your pcie slot to x8 ?

Sometimes you can change it in the BIOS. Not sure if it's my current mobo or the previous where I could do this.

4890 worked with no issues at x8

As long as you can fit it into the slot it should work at any speed. I once put my HD 3870x2 into an open ended x4 slot and that worked fine. I had to flash the BIOS on it because the card wouldn't output anything without a driver on the old BIOS, so text mode didn't work at all, and the BIOS had to be flashed in pure DOS mode. So I had to put it into the x4 slot and put another card in the x16 slot so I could see what I was doing.

 

[almighty]

Run some more tests with a 4870x2 running x8 vs x16 and the difference is 1% at best

 

[Kyyla]

Looks like I shouldn't worry too much about the performance hit of running my 4890 on an old PCI-E 1.1 16x mobo.