Do you need the SLI cable for SLI?

Good morning gents. I pose the question because Im thinking about upgrading to two gtx280ms for my Area 51 M17x. The 280 in the MXM 2.1 form factor wasnt offered with the SLI conection.

I experimented with my dual 9800m gt's last night, I unplugd the SLI cable, and set the card to force rendering 2. I enabled the SLI visualation and it apeared that infact both cards were running. THE FPS was the same as when the cable was installed and the SLI visual was indicating that SLI was working. I used the most recent Star Wars game which is a demanding beast and I didnt see a degrade in perfomance.

When I used just one card, good God the game was un-playable.


My doubt comes from the fact that the slave card was almost 10c cooler at 62C than when the conector was utilized and its GPU load indicated 0% via GPZ. SO is the second card being used, just not as effectively with out the SLI conector?

PS
Im aware of the heat issue, but I think the Area 51 M17x with its dual direct fans can handle it. It seems either you got a lemon or a beast with the old Area 51 M17x, I was a lucky one.

 

I just know that some desktop cards didn't really needed the SLI cable to work, they were able to communicate via the PCI-E Bus. But afaik this really depends on the cards bandwith... when there's already a lot of image data there's no spare bandwith for the communication and that's where the SLI cable comes in place...

This should apply to notebook cards as well. I recommend using the cable anyway.

Someone please correct me if I'm wrong,

The guy at MXM-upgrade have SLI cables on stock afaik, there you should be able to get one.

 

No, from my own testing on desktop you don't need SLi cable for SLi to work. Performance wise I get about 1fps average higher than without cable. From what I know its pretty normal for the second card to be cooler and lower utilized than the first one. I doubt even if the PCIe bus width is halved from x16 to x8 to reduce framerate, since I also tested those, and weirdly I get 1fps lower than full bus width.

As long as there is improvement when 2nd card is used it will be good enough. You could tweak SLi profile using nHancer because I sometime can get near perfect scaling just by playing with SLi profile (AFR/SFR rendering and compatibility flag).

Those are from my experience. So your result may vary.

 

Thank you for the answers gents. 2 GTX 280ms's ordered!!!! Long live the Area 51 M17x!