Quick question> Crossfire RAM mismatch

[Pendragon]

A guy I know is about to upgrade his PC. He currently has an AMD 7870 and is driving a triple monitors with it. I run crossfire and have done for years so I have suggested that a second card would be a cost effective way of boosting the performance.

So a couple of things need clearing up:

Firstly, an R9 270X will crossfire with a 7870? Same card with new name, right?

Secondly, As there are 4GB 270X available, if this card was primary would there 4GB of VRam for the system or would it default to the lower amount of 2GB of the older 7870?

If it's 2GB then there is little point in spending the extra for the 4GB card, just get a cheaper 2GB model. However 4GB of VRam would help with the high pixel count of a triple monitor setup. There is only a 20 quid difference in price.

 

[barnsley]

Be careful, a 270x is the same as a 7870 tahiti (also known as the 7870LE). A 270 is the same as the 'normal' 7870 . What 7870 do they have?

and I'm not 100% sure but if its anything like SLI, but a 2 gb card and a 4gb card in crossfire, there will only be 2gb between the two that is used.

 

[Morgenmuffel]

It may work but as long you dont try that nobody could say that it works.
Better have 4GB of Vram. My 680´s wont even Start any Game with 3 Monitors in here because of the Vram Limit.

 

[Remmy]

and I'm not 100% sure but if its anything like SLI, but a 2 gb card and a 4gb card in crossfire, there will only be 2gb between the two that is used.

I think each card needs to store all the information about a frame, so the total memory becomes equal to the memory of the card with the lowest memory in the setup, so yeah it would be 2GB.

 

[barnsley]

It may work but as long you dont try that nobody could say that it works.

If you're talking about mixing a 270x and a non tahiti 7870, you can't as they're different architectures.

 

[Morgenmuffel]

If you're talking about mixing a 270x and a non tahiti 7870, you can't as they're different architectures.

I cant even SLI a 680 with a 770 even if its the same Thing....^_^

Flashing my 680´s to 770´s doesnt work too^_^

 

[cooperman]

If you're talking about mixing a 270x and a non tahiti 7870, you can't as they're different architectures.

Aparently you can http://www.legitreviews.com/amd-radeon-7000-radeon-r200-series-mixed-crossfire-testing_126124

 

[jamesriley94]

Be careful, a 270x is the same as a 7870 tahiti (also known as the 7870LE). A 270 is the same as the 'normal' 7870 . What 7870 do they have?

and I'm not 100% sure but if its anything like SLI, but a 2 gb card and a 4gb card in crossfire, there will only be 2gb between the two that is used.

As far as I know, you can't SLI cards with different memory sizes now. I think you used to be able to using 3rd party programs but this doesn't work anymore. You can Crossfire cards with different vRAM but the card with more will reduce to whatever the card with the least amount of vRAM has.

It may work but as long you dont try that nobody could say that it works.
Better have 4GB of Vram. My 680´s wont even Start any Game with 3 Monitors in here because of the Vram Limit.

You should be able to... I used to game at 5760x1080 on a single GTX 670. Something else is going wrong if it won't start.

 

[barnsley]

Aparently you can http://www.legitreviews.com/amd-radeon-7000-radeon-r200-series-mixed-crossfire-testing_126124

I swear the 270 is the Pitcarn and the 270x is the tahiti version. Thats what I've seen elsewhere

 

[cooperman]

AMD just loves to confuse everbody i think lol its about time thay updated there site with a new crossfire grid thay still show the old video cards here http://sites.amd.com/us/game/technology/Pages/crossfirex.aspx

 

[Pendragon]

So what we can gather, we have to identify exactly what type of 7870 he has. Because I thought it was 7850=270 and 7870=270X but you are suggesting different GPU models, is this right? Not only that but different models within the same product range of 7870???

But the general consensus of opinion is that with a mismatch of RAM the lower amount is what counts...

As for some of the answers I do become quite confused as to why people start discussing nVidia and SLi in an AMD crossfire discussion. Oh well forums are magical and confusing places...

 

[barnsley]

So what we can gather, we have to identify exactly what type of 7870 he has. Because I thought it was 7850=270 and 7870=270X but you are suggesting different GPU models, is this right? Not only that but different models within the same product range of 7870???

As I said there are two versions. AMD did that for some silly reason. They aren't the same gpu at all and one is noticibly faster than the other.

 

[cooperman]

So what we can gather, we have to identify exactly what type of 7870 he has. Because I thought it was 7850=270 and 7870=270X but you are suggesting different GPU models, is this right? Not only that but different models within the same product range of 7870???

But the general consensus of opinion is that with a mismatch of RAM the lower amount is what counts...

As for some of the answers I do become quite confused as to why people start discussing nVidia and SLi in an AMD crossfire discussion. Oh well forums are magical and confusing places...

The up comeing R7 265 is a overclocked HD7850 but you can crossfire a 7850 with a 7870 crossfire conditions are not as tight as as SLI.
SLI you need 2 cards pretty much exactly the same and a min of x8 x8 speed pcie x16 slots.
The R9 270 is basicly a HD7870 that needs less power the R9 270X is a overclocked HD7870.

http://www.tomshardware.co.uk/radeon-r9-270-review-benchmarks,review-32824.html

 

[NeverBackDown]

A 270 and a 270x are the same card.. a 7870. 270x just has a higher clock speed and instead of one 6pin PCIE connector it has two.

A 7870LE has 1536 stream processors compared to the 1280 the 270 and 270x have. So yes a 7870 will Xfire with a 270x/270.

The newer 265 is a rebuilt 7850, hence why it has the 1024 streaming processors. Though it has improvements in clock speed and such to perform slightly better.

 

[Pendragon]

It's a confusing subject with very little help from AMD on the matter.

 

[NeverBackDown]

Its not confusing when i just explained it... Don't need AMDs help when the spec sheets are out.

 

[RadeonHDx]

I am personally running a setup where I have triple monitors, a 7870 and a 270(non-x). I'm not sure if I have a bad card or its a bug but I can't actually run crossfire without insanely bad artefacts. IMHO I would recomend what I am doing and sell the 7870 and get a 290 if he has a bit more cash to spend.

The 7870 should get around £100-£120 if your lucky and the cheapest 270 (which I got) was £135, so that puts you at £250 for a £300 GPU.

If he has the money and patience to sell the card then tell him to get a 290, if not be wary that you may have some real problems with crossfire.