6xxx series crossfire. Do they combine RAM

[the shoe]

I just ordered a 6870 1GB thinking I would be able to later crossfire a second 6870 and have a combined 2GB of RAM. Is this not the case?

 

[rc51kodiak]

I was wondering the same thing, this thread says that it doesnt so now I am really confused.

http://www.tomshardware.com/forum/245454-33-crossfire-faqs

 

[4745454b]

Not in the way you're thinking of. Sure the combined GPU ram in your system is 2GB, but you still have two chips using it so you also still have 1GB of GPU ram per GPU/chip. This means the same limitations apply. They still have not come up with a way to merge the memory of the cards so that data doesn't need to be stored twice.

 

[the shoe]

Thanx for the replies guys.
Im kinda new to this.
Eventually Id like to run Eyefinity triple monitors, where I heard it takes more memory to do so over one monitor. Would I have been better of just getting one card with 2GB of RAM. Say a 6950/70 2GB?

 

[Helltech]

Yes, two gigs of ram would help very much in eyefinity as opposed to one gig.

 

[soundefx]

This is good to know.

I was wondering where the cut off was in terms of having too much memory. Not too long ago, having a 2gigs of gpu ram was over kill.

 

[4745454b]

True, and for many games it still is. Hardocp has a few games that show you need more then a gig. The 2GB cards are really for those few games, and for massive Eyefinity setups. You can't stitch 3 1080P screens together and enable 8xAA with a 1GB card with modern games. You will run out of ram and experience slowdowns.

http://www.hardocp.com/article/2011/01/11/amd_69706950_cfx_nvidia_580570_sli_review/2

(look at the 6950 and GTX570.)

 

[masteryoda34]

In a crossfire configuration, each card maintains its own copy of data in its own memory. Therefore, the memory is not really doubled. E.G. If a rendering process requires the graphics card to hold 1.5GB of data in memory, and the card is 1GB, adding a second card will not resolve the real issue. However, this is an uncommon issue for games, unless very high resolution is being used.

 

[jprahman]

Correct, each card holds a mirror image of the contents of the memory of the other card, with two 1GB cards the actual capacity is 1GB because of the mirroring. It's kinda like RAID 1, where the total capacity of an array is the size of the smallest hard drive.

For some reason a lot of people get confused and think that the VRAM capacity get doubled.

 

[17seconds]

If there is one lesson to be gained from the reviews of the new 1GB 6950 is that it's performance is almost identical to the 2GB version, even at higher resolutions. Eyefinity is looking like the main reason for getting the 2GB version.

Quote:
"So first off, did you guys check the difference in-between the 1GB and 2GB 6950 versions as well, yeah ... the results are nearly NIL. The added benefit of an extra full GB is excruciatingly hard to measure, even with all games setup with the best image quality settings, hefty shaders and massive textures. The reality is that for 98% of you with today's games 1 GB is absolutely sufficient.

Why would you opt 2GB you might ask yourself ? Well, there are several scenarios, first off very simply, being future proof. In time games will be more demanding when it comes to things like texture requirements. But a more important reason would be multi Monitor gaming, thus Eyefinity. It's there where you breach any foreseeable limitation versus resolution and that's where the extra memory can come into play."
http://www.guru3d.com/article/radeon-hd-6950-1gb-vs-geforce-gtx-560-ti-review/18

 

[rdritchey14]

this may be an old thread but its useful, and heres some info comparing the 6970 and 580.
this is a better bench comp, and basically contradicts the previous link. but i agree for looking for a 2gb high perf gfx card to be future proof.