can 3870s and 3850s be mixed in Crossfire?

[50bmg]

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.

 

[4745454b]

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.

 

[nurn]

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

 

[4745454b]

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.

 

[T8RR8R]

Here's your answer. http://www.driverheaven.net/reviews/3870-XXX/mixed.php

I also read an article somewhere else that mixed a 3850 and 3870 and it works too.

 

[jevon]

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???

 

[hcforde]

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!!!

 

[4745454b]

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.

 

[T8RR8R]

I'm pretty sure that the faster card slows down to sync up.

 

[jevon]

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!!

 

[T8RR8R]

A little more about Crossfire and CrossfireX. http://www.hardwaresecrets.com/article/391/6

 

[hok]

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

 

[T8RR8R]

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.

 

[hok]

I'm so pissed off at my crossfire setup.

 

[T8RR8R]

I'm so pissed off at my crossfire setup.

Let it out man, it's okay.

 

[xbanzai89]

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.

 

[T8RR8R]

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.

 

[rammedstein]

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)

 

[4745454b]

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?

 

[T8RR8R]

I'm sure if I dig I could find more but here is what I came up with so far.

http://ati.amd.com/products/crossfire/faq.html

 

[T8RR8R]

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.

 

[4745454b]

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.

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.

 

[T8RR8R]

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.

 

[hok]

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....

 

[T8RR8R]

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.