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Crossfire 6870 Faster than Single 7970?!

slughead

slughead

macrumors 68040
Original poster
Apr 28, 2004
3,107
237
So I'm soon to be the proud owner of Two 6870s (long story). I do all my gaming in Windows and I usually wait for a few updates/price cuts to play the latest games, so Crossfire is definitely on the table.

Obviously the 7970 ($600-700)is not OS X compatible yet, but while we're waiting I wanted to look at what Crossfire is capable of. Apparently the CF'd 6870x2 do VERY well compared to the single 7970! Look for 6870 CrossfireX (X2 is something else):

BFBC2
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Metro2033
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Now if someone could just tell me if Audio on the HDMI works, I'd be in business!
 
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ActionableMango said:
What did you decide to do for powering the second card?
Click to expand...

I adapted an external PSU using a relay to sync it to my mac pro. Here is it working with my 4970 before the card decided to overheat for no reason.

Edit: Btw, this works absolutely perfectly with my 5870. I just played a game of infinite resources starcraft (HUGE armies, my 2006 MP got down to 3FPS) and there was nary a hiccup!

ext_PSU-Schematic.jpg


ext_PSU-PSU Relay.jpg


ext_PSU-MP Power Output.jpg


ext_PSU-Card Leads.jpg


ext_PSU-End Product.jpg
 
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derbothaus said:
This.

And this:
http://www.extremetech.com/computin...ign=Feed:+ziffdavis/extremetech+(Extremetech)
Click to expand...

As far as minimum FPS, that does seem to vary more with XFire systems, but from the reviews I've read, similar Xfire systems do very well (hardwareheaven.com had a great comparison of CF 6950 Vs single 7970 where the min framerates were still better... cannot find at the moment).

I read a bit about users experiencing microstuttering. Apparently most of the time, when it even occurs (depends on your setup), it can be fixed by setting a maximum framerate around 59-60 in games (a quick google search yields that almost all FPS games are capable of this). Since LCDs only do 60FPS anyway (and the human eye only sees 1/3 of that), this isn't noticeable problem after the adjustment is made.

Another thing to note when reading forums and such is that there are a TON of fanboys out there regarding video cards. On 2 forums I read, people chimed-in on comparison conversations between low-end Xfire setups and the single 7970 with silly remarks like "Get the 7970! It's a great card and you can always add a second one!"... yes, because everyone's got $1600 to spend on video cards. People are going to try and defend their purchases. This is especially true across brands (NVidia Vs AMD), however SLI is apparently a way better implementation than XFire

Me? I can't afford a 7970 and this 2nd 6870 just dropped in my lap. I have no loyalty to either configuration. My choice is between keeping my single 5870 and having dual 6870's--at least until my situation changes (when Apple starts supporting the 7970 and I save some $$$). Depending on the amount of bugs, I'm going to make my decision when my card arrives in a few days.

The 7970 is an amazing card, for sure, but is it worth the money? Probably not, especially with the 7990 poised to be far better when it is released next month and these Crossfire options closely tailing/matching/beating them in many areas at HALF the cost. Would I pay $300 to avoid 5 minutes of inconvenience in googling solutions periodically and not being able to run certain games until 2 months after they're released? My time is not that valuable at the moment :) That's not to mention that the 7970 doesn't work in OS X yet, and likely wont until March/April at the earliest.
 
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I wasn't trying to make you feel like you needed to defend anything. I did the whole SLI/ Xfire thing years ago. I had so many issues with drivers (seriously I had to install and uninstall based on a variety of games. All in I had 4 driver bundles I had to swap in and out of) I gave up on it as too tedious. All the new games ran on 1 GPU until months later they got a correct profile going. For a quick bump to existing it is just fine but not for someone getting into a new system. I always go single card now with no exceptions. It also depends greatly on how affected you are by the micro stuttering I am very sensitive to it. It is pretty widespread as it is a deficiency with the communication between the GPU's. If they would change the bridge mechanics it could possibly be fixed.
 
derbothaus said:
I wasn't trying to make you feel like you needed to defend anything.
Click to expand...

No, not at all! I had the same discussion in my head when I was reading about this last night. I was definitely skeptical about Xfire and was merely trying to glance into the possibility. I found having an open mind and hearing from people who acknowledge the flaws and then overcome them is more useful than just being stymied by the fact that there are flaws at all.

From what the power-users say on the gamer boards, the issues almost always get worked out within 2 months, but they're pretty much inevitable with each new game release (but on the other hand, don't all games get released with bugs?). I'm not denying that Crossfire has serious issues with prompt driver updating, but eventually they do get ironed out. Until they do, you merely turn off crossfire and run at a lower speed for a while, or save your money and buy the game at a discount 2 months later.

derbothaus said:
It also depends greatly on how affected you are by the micro stuttering I am very sensitive to it.
Click to expand...

I definitely can't stand microstuttering, it drives me nuts. However most user reports from people who have actually tried to fix it say it's fixable by setting a max framerate or other changes which don't effect gameplay in any humanly-detectable way.

There are lots of pros and cons, to be sure, but there is no dealbreaker unless you absolutely need to play the latest games the day they come out--and even then, you still can, just by un-linking your cards via the control panel and accepting a lower framerate for a month or two while ATI releases a fix.

This thread wasn't to say crossfire low-end cards are better than the high-end single cards, just that they're faster and cheaper, but not without caveats. Not only that, but the 6870 has the added advantage of being fully OS X compatible (after flashing), even if crossfire is windows-only.
 
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slughead said:
I adapted an external PSU using a relay to sync it to my mac pro.
Click to expand...
Do you mind giving me more detailed info about which parts to buy and a more readable schematic? I need 4x8pins PCIE with external power, otherwise my mainboard will kiss me goodbye :)
 
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