Crossfire and SLI not the same??

kppanic · 22 Sep 2008 at 15:16

4850-4850 vs 4850-4870

Hello,

I've read somewhere (probably a credible source

) that the way Crossfire and SLI work are slightly different, where cards in SLI mode have to be performing identically even if they have different specs. For example, "SLI'ing" a 260 and a 280 would make 280 perform at a 260 level because there needs to be a 1:1 sync (260 one frame, 280 the next). Crossfire, OTOH, does it such that if a 4850 and a 4870 are "Crossfire'd" they would do their fair share of work, as lets say if there was a 25% performance advantage for the 4870 over the 4850, it would do that much more work. (splitting the screen in 40-60 for example?)

The common concensus around the forums, however, is that 4850-4870CF would perform indentically to 4850-4850CF.

Is this substantial?

Cheers

thegoonden · 22 Sep 2008 at 16:08

It's all bunk anyway as both only work in a handful of games.

kppanic · 22 Sep 2008 at 16:09

=/

Presently if 4870-4850 CF is in between 4850CF and 4870CF it actually is a very appealing upgrade path....

kppanic · 22 Sep 2008 at 16:10

I must have been sleep deprived when I read that Crossfire is more advanced than SLI... Argh!

mdjmcnally · 22 Sep 2008 at 16:20

Sounds rubbish to me

I have only ever heard of SLI working in pairs ie 260 and 260, or 8800GT and 8800GT, never heard of anyone have a 8800GT and 8800GTX for instance SLI'ed and working. Certainly Nvidia have always said that need the two cards to be identical. At one point you needed to ensure were the same manufacturer or BIOS flash so had the same BIOS on both.

SLI splits the screen as well, it doesn't have the cards draw alternate frames.

3dfx SLI used to have 1st card draw 1,3,5,7 lines etc with card 2 doing 2,4,6,8 lines etc. Worked well and didn't need fancy support to do it either.

Crossfire has always been more flexible ie 3850 and 3870 however it meant that the 3870 would perform as a 3850.

kppanic · 22 Sep 2008 at 16:33

mdjmcnally said:
Sounds rubbish to me

I have only ever heard of SLI working in pairs ie 260 and 260, or 8800GT and 8800GT, never heard of anyone have a 8800GT and 8800GTX for instance SLI'ed and working. Certainly Nvidia have always said that need the two cards to be identical. At one point you needed to ensure were the same

My bad on that, what I meant to say was that SLI was designed such that only two identical cards work. Didn't mean to say I'd tried to fit a 260 and a 280 =) I always thought SLI had to have the work split 50/50 (one card every even line, and other other odd lines) where as Crossfire would be more like 4850 takes 40% of the lines whereas 4870 would take the other 60%.

Hmm so there was absolutely no point for ATI/AMD to allow the end users to even Crossfire two different cards in the first place. If I were AMD i'd just make the users get two identical cards just like nVidia instead of allowing two dissimilar cards to run together. Liars.

kylew · 22 Sep 2008 at 17:18

Uhh?

You can mix and match with crossfire. If you mix a 4870 with 4850 they run at their own speed, neither one has to change to accommodate the other.

As for multi-GPUs working in a 'handful' of games, we all know that's fantasy talk going on there thegoonden just because you seem to dislike multi-GPU setups. In reality it's a handful of games that don't work with sli or crossfire.

You've also now got games that are scaling 100% with crossfire. I suppose I'm one of the 'lucky' ones who is yet to notice any sort of 'micro-stutters' with multiple GPUs, I just must not be prone to it.

People have been running 3870s and 3850s together for sometime, and 3870X2s and 3870/3850s. You can mix and match cards from the same line. So that's 48XXs with 48XXs, 38XXs with 38XXs without one card being held back by a 'slower' card, the load is just split accordingly between the cards. So maybe it could be 60/40 split between a 4870 and 4850 in crossfire.

psychas · 22 Sep 2008 at 17:23

single card solutions is less problems. i had 3870cf and it was dreadful loads of problems

LoadsaMoney · 22 Sep 2008 at 17:41

kylew said:
Uhh?

You can mix and match with crossfire. If you mix a 4870 with 4850 they run at their own speed, neither one has to change to accommodate the other.

As for multi-GPUs working in a 'handful' of games, we all know that's fantasy talk going on there thegoonden just because you seem to dislike multi-GPU setups. In reality it's a handful of games that don't work with sli or crossfire.

You've also now got games that are scaling 100% with crossfire. I suppose I'm one of the 'lucky' ones who is yet to notice any sort of 'micro-stutters' with multiple GPUs, I just must not be prone to it.

People have been running 3870s and 3850s together for sometime, and 3870X2s and 3870/3850s. You can mix and match cards from the same line. So that's 48XXs with 48XXs, 38XXs with 38XXs without one card being held back by a 'slower' card, the load is just split accordingly between the cards. So maybe it could be 60/40 split between a 4870 and 4850 in crossfire.

Correct, so if your running a 4850 with a 4870 in Crossfire, then they will be faster than 2x 4850's.

Crossfire is more advanced than SLi, mix and match, dual screens, Nvidia can't do any of that, when you pair 2 identical series Nv cards (i.e 8800 GT + 8800 GT), if ones a slower speed, then the other one has to downclock to match it lol, or the slower one clocks up to match the faster one (as long as the faster on is in the primary slot i think).

They are adding Dual Screen Support for SLi in their upcoming 180 drivers though.

kppanic · 22 Sep 2008 at 17:53

LoadsaMoney said:
Correct, so if your running a 4850 with a 4870 in Crossfire, then they will be faster than 2x 4850's.

Crossfire is more advanced than SLi, mix and match, dual screens, Nvidia can't do any of that yet, they are adding SLi dual screen support in their upcoming 180 drivers though.

This is awesome news =)

I just wonder why I have not seen a single substantial review of mixed cards, as I strongly believe 4870+4850CF is a very flexible upgrade path for a lot of people, including myself. However when the 4850x2 releases or as the prices of 4870/4850 come down substantially in the next year or so, 4870+4850CF might not be an ideal choice though.

Anyway this is awesome, I won't have to go through selling the 4850 in the future to play games at 24"+ or at 1900x1200 4xAA 16xAF =) I'll just add a 4870.

Strife212 · 22 Sep 2008 at 17:57

thegoonden said:
It's all bunk anyway as both only work in a handful of games.

Your idea of handful of games must be different to mine

3dcandy · 22 Sep 2008 at 17:58

sure I have seen a handful of places that crossfired different cards. however i'm more interested in hybrid crossfire with a 780g or 780gx chipset and a 4670 or something...now that would make a sweet htpc and games machine a lot easier to build

LoadsaMoney · 22 Sep 2008 at 18:00

http://www.fudzilla.com/index.php?option=com_content&task=view&id=9535&Itemid=1

4850X2's on hold, must be nice not having to launch when your others doing so well.

kppanic · 22 Sep 2008 at 18:08

3dcandy said:
sure I have seen a handful of places that crossfired different cards. however i'm more interested in hybrid crossfire with a 780g or 780gx chipset and a 4670 or something...now that would make a sweet htpc and games machine a lot easier to build

Linky linky?

3dcandy · 22 Sep 2008 at 19:56

erm...yeah....can't remember!!!!

Final8y · 22 Sep 2008 at 20:45

thegoonden said:
It's all bunk anyway as both only work in a handful of games.

Don't get me started !
50 games here & CF on my 4 x 3870 does not work on 2 of them.
EDIT: Actually your nick rings a bell & i had this out with you before & at the time it was just as the 3780 line was launching & i said that i predict that multi GPU will be more popular on this forum than ever before.
And now it is.

LoadsaMoney · 22 Sep 2008 at 21:05

CrossfireX and SLi is supported in just about everything now lol, and wasn't it Anandtech who did the CrossfreX mix.

thegoonden · 23 Sep 2008 at 04:21

All current games may support these things, yes.
But some of us play older games too. I'm as likely to spend an hour on Crysis Warhead or GPL, as likely to play GTR-evo as MS trainsim (to hell wieth crysis, if you want a game that buckles a computer, that's your boyo right there).

Rroff · 23 Sep 2008 at 04:50

mdjmcnally said:
Sounds rubbish to me

I have only ever heard of SLI working in pairs ie 260 and 260, or 8800GT and 8800GT, never heard of anyone have a 8800GT and 8800GTX for instance SLI'ed and working. Certainly Nvidia have always said that need the two cards to be identical. At one point you needed to ensure were the same manufacturer or BIOS flash so had the same BIOS on both.

SLI splits the screen as well, it doesn't have the cards draw alternate frames.

3dfx SLI used to have 1st card draw 1,3,5,7 lines etc with card 2 doing 2,4,6,8 lines etc. Worked well and didn't need fancy support to do it either.

Crossfire has always been more flexible ie 3850 and 3870 however it meant that the 3870 would perform as a 3850.

nVidia SLI can work in both SFR and AFR modes, can even do combination modes if you have more than 2 video cards.

3DFX SLI was limited to triangle setup/rendering and didn't really handle geometry, etc. with modern GPU features sets 3dfx SLI would be mostly useless as fillrate generally isn't an issue any more except in scenes with a lot of smoke, etc.

It is possible to SLI different cards in the 8 series line, even easier if they are both based on the same core i.e. G92 - but its not for the faint of heart - at the very least you will need to hand modify the GPU BIOS files - it is even possible to run cards in SLI at different speeds - but again I don't reccomend it - you will feel the wrath of "micro-stutter*" - which can also be a big downside to crossfireX with mis-matched cards.

* "micro stutter" is generally over hyped but in specific circumstances it can be noticeable.

kylew · 23 Sep 2008 at 11:32

thegoonden said:
All current games may support these things, yes.
But some of us play older games too. I'm as likely to spend an hour on Crysis Warhead or GPL, as likely to play GTR-evo as MS trainsim (to hell wieth crysis, if you want a game that buckles a computer, that's your boyo right there).

Doesn't that kinda make your point null though? Why would you need crossfire/SLI for old games? They'll run more than good enough on a single card. Just turn crossfire off when playing those old games that don't support it?

Or, if crossfire doesn't give any improvement, just leave it on as long as it doesn't bring the performance down.

How many FPS could you really need? A game as recent and good-looking as portal, ran at max settings on my PC when I had a 3870X2 would regularly be over 200FPS, with 8XAA/16AF @1920x1200.

All those old games would have their FPS in the thousands on the newer graphics cards out.