Bitcoin Forum

I am building a system with 2 x 5870s.  Do I need to use a dummy plug or just set them up in Crossfire to hit 800Mh/s?

Don't bother with crossfire and put a dummy plug in one if you have a monitor in the other.  If you are just setting it up to run then throw a dummy plug in both.  I have a mining rig in my basement that has four cards in it and they all have dummy plugs.  I use VNC from my gaming machine if I need to configure something.  No need wasting a monitor on a mining rig.

This is going to be my main computer as well.  Just figured I would run the miner when the computer was idle (which is most of the time).

Do you use one monitor or two?  If two, no need for dummy plug... if one than everything that I have read suggests to not use crossfire.  In this case you will need a dummy plug.  Dirt cheap and easy to make.

I use 2 monitors so I assume run it in Crossfire and run 1 monitor off of each card?

never used ATI before, but if its like Nvidia you don't need to link em, just one monitor in each card

It's so the card "is on" (in a matter of speaking) We've been doing this for a few years in the folding side of the house, super cheap and easy to make a dummy if you ever chose to tho

Crossfire is like SLI... if you have two monitors though, don't use crossfire.  Just plug one monitor into each and you do not need any dummy plugs.  The miners get better hash rates without crossfire.

If you have a monitor with dual inputs(VGA/DVI) just run a cable from each card to one of the inputs.  Works fine for me.

Are there any numbers, regardless this?

So, you need a dummy plug for a modern video card to work? Oh well, I guess I'll make one, since I intend to run the mining PC headless (with remote control). I never had that problem before, that is, up until now, I ran some PCs headless and they worked fine, I guess it's something new or the drivers do not like the fact that there is no monitor. The plug should be easy to make though, AFAIR a couple of pins need to be shorted.

The dummy plugs are only required for Windows.  If you're using Linux, they are unnecessary.

That's the thing. I am using Windows and before I got a bigger KVM switch I just kept the PCs with no monitor connected and connect it only when something broke (and /i could not use remote control to fix it). Though again, maybe it is applicable only to mining and only on new cards.

In case someone is still out of the loop, dummy plugs are now redundant.

AMD is fixing the issue with the 11.7 drivers so GPUs will be detected without being plugged into monitors (or dummy plugs being used).

You can already download the 11.7 preview drivers online.
http://www.geeks3d.com/forums/index.php/topic,2195.0.html

This is good news!

in a pinch you can move the monitor from card to card and force detection, this only works until the next reboot of course

Or if you have enough different cable  hook ups to your monitor you can run a hdmi/dvi/vga one cord to each video card and it will force the video.

I have 2 5970's in crossfire (4 Gpus) I have bench marked with 3 PLANAR 27 inch in crossfire with an eyefinidy dispay group resolution of 5760x1080 running various different settings ...I saw no difference at all vs just 1 monitor at 1920x1080 or even all the way down to 640x480 res 16 bit.  No difference at all. getting 369-377 on all for cores at 900/500.