Bitcoin Forum

If im mining with 2 ati cards, do I put on the crossfire bridge between the two cards, and do I enable crossfire? Or just run the two cards as separate workers?

6 million posts already talking about this, but I'll answer it anyway and kindly request that you use the search function next time.

If you use Linux you don't need to Crossfire and the OS will see and use both cards.

If you use Windows you don't need to use Crossfire, but Windows won't see the second card unless it thinks there is a monitor on it. This can be spoofed using a VGA dummy plug. http://www.geeks3d.com/20091230/vga-hack-how-to-make-a-vga-dummy-plug/ (http://www.geeks3d.com/20091230/vga-hack-how-to-make-a-vga-dummy-plug/)

I have 3 ATI cards all running on Windows without Crossfire.

ok... but will crossfire increase or reduce mining speed compared to not using crossfire? or is there no difference? In which case is there any reason for me to use or not use crossfire...

There's no difference. The only difference is in the cost between the dummy plugs and the crossfire bridge.

I thought all ATI cards come with a bridge... mine did anyway, so I should just use the bridge then?

Not tested personally, but others state that Crossfire reduces the MH/s when compared to individual cards.

interesting, can anyone confirm/deny?

I can confirm that CrossFire affected mining speed on my 2x5870 rig. With CF bridges installed and CF enabled hashing speeds used to vary wildly between the two cards. Now I run with CF disabled and CF bridges removed but had to connect both cards to a KVM switch since I'm too lazy to go to the store and buy 6 resistors. Hashing speed is now constant and equal on both cards. I mine with Phoenix with phatk kernel and both 5870's run at 935/320.

One side note: CPU usage is at 100% under Windows, no matter if CF is on or off.

The crossfire bridge can make windows see both cards without the use of dummy plugs. so If you've already got the crossfire bridge, use that.