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noob needs help understanding crossfire

lau808

Senior member
Jun 25, 2011
217
0
71
i dont really understand crossfire yet, i understand that 2x 6970 is practically a 6990 but... i assume thats in a x16 x16, but what about in a x8 x8? and while a card with 500 sp in crossfire is now 2x500 is that the same as a card with 1000? any help with this is much apreciated, also if u post links to articles i will gladly read them, thanks in advance :)
 

Madcatatlas

Golden Member
Feb 22, 2010
1,155
0
0
The following is my own "idea" of how CrossfireX works. I might be really wrong ;)

Its basicly a doubling of all numbers except VRAM, which is each cards memory. This stays at the lowest cards amount for each card. What this means, is that if each card has 1gb Vram, this will stay the same also while they are crossfired. Ive understood that there is some traffic between both cards Vram when rendering screens.
If one card has 2gb Vram and the other has 1gb, both will be capped at 1gb each.

Concerning the split of PCIe lines, apparantly the difference between x8 and x16 is not a whole lot at all. Ive read differences of about 1-3% if anything. Normally something else is the "bottleneck" or there is no bottleneck because the lanes dont get saturated/filled.


Its not much i admit, but its what little i have gathered.

The downside to having multiple graphics cards in any configuration, is that although you have more power available, not every game or application will use that power. And for such multiple card configurations, both AMD and Nvidia have profiles which they update frequently.

Im sure you knew alot of the stuff i just wrote, but hey, im just trying to help out! ;)
 

Puppies04

Diamond Member
Apr 25, 2011
5,909
14
76
As far as i have read (there is a whole host of information on this if you feel like using google) 2*6970 is actually faster than a 6990 unless you flip the overclock switch on the 6990 and void your warranty. Basically they weren't prepared to have the cards running at 100% as they generated too much heat and drew too much power. On the x16 x16 vs x8 x8 debate there really isnt much difference and i would guess that even only taking into acount "gamers" 90%+ machines out there dont have the 32 lanes avaliable for x16 x16 anyway.
 

lau808

Senior member
Jun 25, 2011
217
0
71
thank u both, that helps a lot. i googled (1 page worth) and didnt find all the info i wanted on crossfire, i did see that 2x6970 are slightly faster tho. i guess i could have explained a lil more but basically i am looking to my 1st build later this year and so far plan on getting a sabretooth mobo even tho i only need a cheap 980g. i run 2 monitors so i wanted to have this info handy when i decide between 2 cheap cards or 1 card that has 2 dvi outputs. even tho i dont have special needs for graphics i cant help but wanna know exactly whats goin on with my choices
 

darckhart

Senior member
Jul 6, 2004
517
2
81
CF on a single card is like SLI on a single card. The gpus get to talk to each other using a chip on the card before going thru the mobo. CF with two cards means they talk to each other thru the bridge before going thru the mobo. as i understand it, a 6990 is really 2x6970 running at 6950 clocks, hence why 2x6970 cards is faster.

In any case, unless you have a minimum of 19x12 screen res with inane eyecandy and AA settings, a CF setup is overkill. For what you mentioned, a single card from ati supports up to 3 monitors, each using a different connector (1xdvi, 1xhdmi, 1xdp) (albeit you may need a fancy active dp cable for that 3rd monitor if it doesn't have a native dp connector).

I assume most people that purchase CF (or SLI) fall into 3 categories:
1. need the ultimate gaming power right now (and possibly for multiple screens)
2. need 2 cards to make the equivalent (or better) performance of a better single card for a cheaper total price
3. held onto that single old card for so long that picking up another one is dirt cheap compared to spending for a new single card because that new next gen card is "right around the corner" so let's make this rig last a few more months.
 

lau808

Senior member
Jun 25, 2011
217
0
71
ah yes, the 6990 vs 2x6970 was just an example, i know i dont need that type of performance. 2 of the cheapest cards will be more than sufficient as would onboard 4250/90 had the 990fx came with integrated graphics. but i will spend a lil on a single or 2 card setup just for kicks but mainly wanna know what im buying when i compare :)
 

Puppies04

Diamond Member
Apr 25, 2011
5,909
14
76
What are you planning on doing with this pc? Talking about crossfire then commenting that a 4250/90 would be sufficient has me confused... you are aware that onboard graphics is completly underpowered for any sort of decent 3d gaming aren't you?
 

lau808

Senior member
Jun 25, 2011
217
0
71
lol yes, i jus want 2 dvi outputs but was curious and wanted to further understand all the numbers behind crossfire x16 x16 and x8 x8 as im a lil bit of a numbers guy. i wont do anything special with this pc . was basically gonna compare 2 cheap 6xxx cards vs a decent 6xxx card with 2x dvi and choose based on price diff and specs. by the time i do my build i might just say f*ck it and buy a good card just to have one(6950?) but i know i dont need performance as i am jus an enthusiast that wants but doesnt need more than my current athlon II x2 3ghz pc . either way, i love understanding/learning all about these things tho and what they mean
 

lau808

Senior member
Jun 25, 2011
217
0
71
oops, forgot to mention, this pc mainly plays online poker, browse internet, watch youtube, and listen itunes. poker hand history database program while playing takes advantage of 4 cores and ssd if available, everything else is gravy
 

Puppies04

Diamond Member
Apr 25, 2011
5,909
14
76
oops, forgot to mention, this pc mainly plays online poker, browse internet, watch youtube, and listen itunes. poker hand history database program while playing takes advantage of 4 cores and ssd if available, everything else is gravy
Sounds like you don't even need a GPU :D get a chip like an I5 2500k for example on a H67 board and you can run all those programs at once on dual monitors.
 

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