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can 3870s and 3850s be mixed in Crossfire?

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  • Radeon
  • GPUs
  • RAM
  • Crossfire
  • Graphics
Last response: in Graphics & Displays
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December 11, 2007 7:19:39 PM

can 3870s and 3850s be mixed in Crossfire?

I read a review on Newegg.com earlier. He said he had a 3870 and a 3850 in crossfire. I thougth GPUs or RAM amount couldn't be mixed. Only that manufacturers could be mixed as long as they both had the same amount of RAM and same GPUs.

More about : 3870s 3850s mixed crossfire

December 11, 2007 8:00:14 PM

Quote:
I thougth GPUs or RAM amount couldn't be mixed.


True, except for the 3xxx series from AMD. If you plug a 3870 and a 3850 together in CF, the 3870 will basically turn itself into a 3850. It will reduce its clock speeds, and disable half the memory so that it will work as a 3850. I don't know if the 8x00 series from Nvidia will do this also or not.
December 11, 2007 8:17:13 PM

Check out this chart. To me, it appears that the 3870 can be coupled with a 3850 (judging by the red coloured boxes in the matrix). However, I saw a post from another guy who also referenced this same chart as proof that they could NOT be coupled together. I would like to see the link to the newegg.com post.

http://ati.amd.com/technology/crossfire/charts.html
Related resources
December 11, 2007 10:09:00 PM

I don't see how you can reference that chart, and say you can't do it. The dot says the 3870 is the recommended card for the 3870, while the red rectangle is a possible card. All of the white rectangles are cards that won't work. If the 3850 wouldn't work, it would be white and not red.
December 18, 2007 10:14:15 PM

Pretty sure the point of CrossfireX (on the 3xxx cards) is to allow 4x GPU in Crossfire, and to allow a mix and match between models with no performance loss - ie, if you read the extremesystems forums and what they're doing over there, I dont think the 3870s 'downgraded' themselves under Crossfire...they were talking about how great it will be to add in newer ATI cards over time to the 16x slots and bump the 3870 and 3850s back along the PCIe lanes (to the slower 8x's on the 790FX boards). I could be wrong and I didn't save the link to the guys who were crossfiring the 3850 and 3870, but do you have any links saying they do downgrade to a 3850 level like ram would if you mix and matched them???
December 18, 2007 10:32:05 PM

I think some of the confusion is the understanding of the original Crossfire and CrossfireX. There is also things that were to be implemented and were not, so the capabilities of these different protocols need to be defined by AMD/ATI. We were suppose to be qable to add acard to the crossfire setup to act as a PHYSICS processorwith either 1 or 2 ATI cards doing the rendering of the frames(3 card total). The physics card was to be an x1600 or higher. As I recall if you added 2 ATI cards in the original setup the lower card would rule-thus the higher performing card would be downgraded. In CrossfireX that may be different as it is a different protocol. It may work 'like' JBOD in RAID where an added drive increases the overall capacity. BUT I DO NOT KNOW THAT THIS IS A FACT!!!
December 18, 2007 10:56:15 PM

Jevon, I don't see how it would work without the fast card downgrading itself. The 3850 can't clock itself up to the faster cards speeds, and if you left the 3870 at stock it would be faster then the other half of the CF equation. Lets assume that it doesn't change anything on the 3870, because it can only work as fast as the 3850, it is effectively turned into one anyways. Take a look around for mixed CF benchies and see what they say.
December 19, 2007 1:55:11 AM

I'm pretty sure that the faster card slows down to sync up.
December 19, 2007 2:25:46 AM

Hmm interesting, I've seen a few mixed benchies on various sites and forums but I can't recall if they actually said whether or not the faster card was downclocked. I'll have to take a few minutes tomorrow to comb through the threads @ ExtremeSystems to see if I can't find the posts that were talking about it.

I myself didn't really understand the 'how' part behind a 3850 and 3870 working together at their respective specs because the point of Crossfire/SLI is to make the cards operate as one single GPU, but from what I had read I thought this was somehow overcome with CrossFireX :o  Very good to know this may not be the case!!
December 19, 2007 2:55:43 AM

Who cares about crossfire... even if you bought two card it doesn't even work
December 19, 2007 2:57:45 AM

hok said:
Who cares about crossfire... even if you bought two card it doesn't even work



Pretty much what he said, but then there are benchies like these http://www.legitreviews.com/article/607/5/
Still a bummer that Nvidia won't allow SLI on Crossfire capable chipsets...sigh. :pfff: 
December 19, 2007 4:46:45 AM

I'm so pissed off at my crossfire setup.
December 22, 2007 12:45:12 AM

hok said:
I'm so pissed off at my crossfire setup.


Let it out man, it's okay.
December 22, 2007 10:10:42 PM

hok said:
Who cares about crossfire... even if you bought two card it doesn't even work

What? Last I heard crossfire scaled a lot better then SLI. Such as the 3870 XFire doing better then the 8800 GT SLI. Only makes sense due to the 3870 X2 coming out and quad drivers. They need to be pretty good so people will buy such setups.
December 22, 2007 11:28:31 PM

Crossfire does have it's issues, but SLI often has even more. The 1 thing that I really like about Xfire is that you can mix 2 different cards.

The more I read into how it works the more I'm finding out that Xfire doesn't force the higher card to perform at a lower spec, nore does it force the lower one to speed up.
December 23, 2007 12:16:31 AM

t8rr8r is tyrue, they just render diffe3rent amounts eachfaster card does more ect, also, you can combine the 2900xt and the 3870 in crossfire, not too sure about the 3850 and 2900xt though (i know for a fact because i have tried)
December 23, 2007 4:29:34 AM

Educate me then please. If the faster card doesn't downclock, or disable half of it memory, how would it work? Can one of you please provide some linkage for the rest of us?
December 23, 2007 10:54:16 AM

Ummmmmm I dunno, but I've been doing my research on the subject recently and I just read an article the other day that clearly stated that 2 cards in crossfire run at their own speeds and they don't have to be the same memory, or speed or anything. They just work together and the higher speed one doesn't clock down and the lower doesn't clock up. I know it doesn't make sense but it's the truth. The fact is that even though 2 cards might be clocked the same that doesn't really mean they are both running at the same speed. Just like if you had 2 computers with the exact same hardware and software 1 would perform slightly better by some degree.

Anyway the best way that I could describe is if you imagine 2 people running in a circle side by side. The one on the outside would have to run a little faster to keep up to the one on the inside of the circle. Just imagine that the technology that makes crossfire work the way it does will force the faster card farther out of the circle. It's not really going any slower is it? NO.

I'm doing the best I can to explain it from what I understand. I don't work in an ATI so I'm no engineer about this.
December 23, 2007 5:14:15 PM

See, thats what I was thinking stranger. Its like AID0. You can use drives of different speeds, but the faster one will be effectively slowed by the slower one. The faster drive will get done doing its task first, then will wait for the slower one. I get the feeling the same would happen in CFX mode. (unless of course you use a 60/40 split or something like that.)

I haven't read the link yet, I'll get on that.

EDIT: Are you sure you meant that link? It doesn't say anything about CFX, only CF. As a matter of fact, look at #8.

Quote:
8. What happens when you pair a 12-pipe CrossFire Edition card with a 16-pipe card?

A. In this scenario both cards will operate as 12-pipe cards while in CrossFire mode.


I know CFX changes some thing, but as stranger and I have said, I doubt this is one of them.
December 23, 2007 6:14:08 PM

9. What happens when your CrossFire Edition card and and a compatible standard Radeon (CrossFire Ready) graphics card have different clock speeds?

A. Both cards will continue to operate at their individual clock speeds.

Hey I'm no officiando of CF or CFX, just that I know what I've read lately because I've been digging trying to understand it all myself. Just as most people on here tell nOObs, try google.
December 24, 2007 12:26:26 AM

yunno it would be interesting to see the scaling that a mixed card setup and comparing to a 3870/3870 setup for instance would provide in terms of performance.

Would the % increase be a lot higher in the identical setup? or just a secondary card is good enough....
December 24, 2007 12:38:37 AM

That's part of this review that I've been trying to find that mixed a 2900xt and 3870 and then compared it to 2 3870's together. It also explained how 2 different cards can work together without changing any of the speeds on the cards. The main focus of the review was for the 3870 so if you guys are looking at 3870 reviews and find it, post it.

I know that the 2900xt mixed with the 3870 didn't really give that much more performance, but still some. However there were a few tests that it really screamed on.
December 24, 2007 12:46:45 AM

AMD FTW! Ugh... no, not really.
December 24, 2007 12:59:09 AM

rodney_ws said:
AMD FTW! Ugh... no, not really.

Yeah, that was helpful.

Anyway there's a link to show you guys that a 2900xt and 3870 will work together, although it's not the review that I was thinking about. It does show you that it can be done and that in some programs it does provide quite a performance boost. http://www.driverheaven.net/reviews/3870-XXX/mixed.php Not as much of an increase as there would be with 2 of the same cards but still pretty sweet for those of us that aren't sure about mixing cards.
December 24, 2007 1:58:21 AM

As strangestranger has pointed out, CrossFire uses alternate frame rendering (AFR). Each card renders its own full frame, one after the other. In order for this to work properly both cards must be functionally identical. This means having the same clocks, same VRAM, same number of shaders, etc.

A 3870 and a 3850 in CrossFire is effectively the same as a pair of 3850s in CrossFire.
December 24, 2007 2:43:47 AM

Actually crossfire uses all methods, Supertiling, AFR, and Scissor. http://ati.amd.com/technology/crossfire/modedemo.html

AFR is like what I was saying earlier by reffering to the 2 people running around a track. 1 card might run slower and the other might be running faster but in the end they are both making a full lap(image) at the same time. In actuallity if you put the 3870 together with a 3850 the 3870 will produce it's "half" of the image faster than the 3850 would therefore mixing a 3870 with a 3850 would be faster than two 3850's.

I'm not saying that mixing a 3870 with a 3850 would be as fast as two 3870's together. I'm just saying that the 2 work together and that mixing a 3870 with a 3850 would place the crossfire speed between 2x3850's and 2x3870's.

The point is that Crossfire can mix GPU's unlike SLI and that mixing a higher and lower end GPU would actually place the setup somewhere between 2 greats and 2 not so greats. In the end this would allow people go get a 3850 because they are really cheap for what you get and then later on get a 3870 when it's cheaper. People would be able to take better advantage of discounts, sales, and higher end cards.
December 24, 2007 1:23:11 PM

T8RR8R said:
Actually crossfire uses all methods, Supertiling, AFR, and Scissor. http://ati.amd.com/technology/crossfire/modedemo.html

Right, but it performs best when using AFR. The main advantage that supertiling and scissor have is the ability to work in almost every game, regardless of whether or not there is a CrossFire profile for that title. They are both slower than AFR.
T8RR8R said:
I'm not saying that mixing a 3870 with a 3850 would be as fast as two 3870's together. I'm just saying that the 2 work together and that mixing a 3870 with a 3850 would place the crossfire speed between 2x3850's and 2x3870's.

I was under the impression that the system could only be as fast as its slowest link. The only way I can see performance ending up between the two GPUs is if the system offloaded some of the slower card's workload to the faster card. That would be a nearly impossible task in my opinion, but I believe AMD is working on something like that with their mixed CrossFire.
December 24, 2007 1:54:14 PM

I think the best benefit from this is, a new generation card doesn't make your current card obsolete. Like Jevon posted above. For example: I have a 3870. When the next generation ATI comes out, 4xxx or whatever, i can put it in the primary pcie slot and move the 3870 to the next pcie slot. It protects my purchase from being a waste of money in 12 months. That is why i like the idea of mixing. Not to mix 2 current cards, but for mixing future gen cards with my current card. That will get me another full year out of the cards i spend my hard earned money on.

2 cards are better than one. It may not be the best use of Crossfire, but i like being able to keep my cards a year or two longer. With CrossfireX and 3 or 4 pcie slots, i can keep them for 2 years longer or as long as they are compatible.

eventually, sooner than later, chipsets and gpus will change architecture and compatibility will be an issue. It is more profitable to obsolete legacy technology so consumers have to buy new technology. But, this will save my cards for a little longer.
December 24, 2007 3:54:31 PM

Maybe 50, we have to wait and see. Notice at the end of the article that t8rr8r posed, they said they suspect it won't work with future driver releases. AMD has decided to allow different cards in the same generation to work, I believe the question is still out if they will allow different cards from different generations to work. It sounds good in theory, but I suspect future cards might be to different from current cards to allow this. (think of what would happen if you tried to mix the 2900XT with the x1950xt, two very different cards. 2900XT and 3870 could work because they are so similar.)
July 21, 2008 12:06:27 AM

50bmg said:
I think the best benefit from this is, a new generation card doesn't make your current card obsolete. Like Jevon posted above. For example: I have a 3870. When the next generation ATI comes out, 4xxx or whatever, i can put it in the primary pcie slot and move the 3870 to the next pcie slot. It protects my purchase from being a waste of money in 12 months. That is why i like the idea of mixing. Not to mix 2 current cards, but for mixing future gen cards with my current card. That will get me another full year out of the cards i spend my hard earned money on.

2 cards are better than one. It may not be the best use of Crossfire, but i like being able to keep my cards a year or two longer. With CrossfireX and 3 or 4 pcie slots, i can keep them for 2 years longer or as long as they are compatible.

eventually, sooner than later, chipsets and gpus will change architecture and compatibility will be an issue. It is more profitable to obsolete legacy technology so consumers have to buy new technology. But, this will save my cards for a little longer.


I agree with you completly as I currently own a HD 3850 512MB and I bought a HD 3870 512MB card, I will move the 3850 to the secondary PCI x16 slot and place the 3870 into the main slot, the only difference is the type of memory, GDDR3 and GDDR4. Is it possible to mix these types of memory?
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