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.

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.

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

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.

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.

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???

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!!!

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.

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

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 Very good to know this may not be the case!!

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

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.

I'm so pissed off at my crossfire setup.