HD4870 512mb and 1Gb Xfire, any issues?

[MouthBoy]

Hey Dudes

Looking to purchase a second HD4870 for my system and have found a 1gb version for a good price. Now from what I have googled, there doesnt seem to be many issues with using a 512mb and 1gb version together. I fully understand that the 1gb will only use 512mb and that the slowest clock speed will be used, but apart from that, anything I should be aware of?

I have also heard that if I used the 512mb as master and the 1gb as the slave, that the slave can actually use all its memory? Is there any truth to this?

Thanks

Scott

 

[reflux]

Two 4870s using 512mb each just ain't really worth it. 1920x1200 or above is where CrossFire is useful, and 512mb of frame buffer isn't really enough at that res.

 

[MouthBoy]

http://www.anandtech.com/bench/Product/162?vs=174

If I am able to get close to HD5870 performace using xfire for a third of the price... I know what your saying though. I have already made up my mind that I will purchase a second HD4870, but I would like to know the answer to the question above.

 

[dwskillz]

I have the 512mb and 1gb mix of 4870's for about 2 years now and have not had any problems atall.

 

[Marine-RX179]

http://www.anandtech.com/bench/Product/162?vs=174

If I am able to get close to HD5870 performace using xfire for a third of the price... I know what your saying though. I have already made up my mind that I will purchase a second HD4870, but I would like to know the answer to the question above.

It really depends on the res you are gaming at. At 1680x1050 or below, you'd have most like have no problem for the CF4870, however if you game at 1920x1080 or above, the lack of VRAM could cripple the performance and frame rate of the CF4870 in some, if not most games. The results you quoted from anandtech, the 4870x2 get 1GB of VRAM per core. When you crossfire the 4870 512MB with a 1GB, the faster with more VRAM card will mirror the slower lesser VRAM card, so you still only get 512MB per core.

 

[DrBombcrater]

You shouldn't have any issues running mis-matched memory sizes. I run a 4870/512 and a 4850/1GB in crossfire and haven't had any problems. A 512MB framebuffer is a little limiting at higher resolutions, but cripplingly so. I find as long as I keep anti-aliasing switched off the 4870 is faster in every game I have than the 4850 at 1920x1200, so the extra vmem isn't that big a deal.

Everything I've read says the extra memory on the 4850 should be ignored when running in crossfire, but I've found differently. In some games running 1920x1200+AA causes a big performance hit on the 4870 alone, but the two cards in crossfire are much faster - not what you'd expect if they were running out of vmem. But I've yet to find any real explanation of why this happens.

 

[uv]

I have also heard that if I used the 512mb as master and the 1gb as the slave, that the slave can actually use all its memory? Is there any truth to this?

No. The smallest framebuffer is always the limiting amount. in terms of crossfire, 1GB + 512MB = a total of 512MB. Think of it like raid0 - the data in memory is mirrored, and any space left over on one unit can't be mirrored onto the smaller unit, meaning it isn't used at all.

4870 512MB crossfire is pointless imo at 1080p, as the extra grunt of another GPU is just going to be held back by the comparatively small framebuffer.

At 1920, it's not the 4870 that's limiting, it's the 512MB - when I switched from a 512MB 4870 to a 1GB one back in the day, I noticed a respectable improvement (especially in regards to being able to apply AA).

 

[thingemajib]

is this 1gb version for a good price being sold independanly, or from a retailer?

if its a retailer, you could always buy two and sell your 512mb one