First Time Crossfire - Help!

[the4thgengamer]

Hi all! I just got a 2nd GPU for my computer, long story short, its a BIT different from my 1st one, but they are pretty similar. Given this is AMD, hopefully that won't be a problem. I will be running these two in a crossfire configuration. I have never done this before, so I'd like to verify that there aren't any other precautions that I should take.

 

My two cards are as follows -

MSI R9 380 GAMING 2G http://www.newegg.com/Product/Product.aspx?Item=N82E16814127876&cm_re=msi_r9_380_2g-_-14-127-876-_-Product

SAPPHIRE R9 380 NITRO 4GB http://www.newegg.com/Product/Product.aspx?Item=N82E16814202149&cm_re=r9_380-_-14-202-149-_-Product

 

So far, both are installed and it looks like they are running fine. I uninstalled the old drivers, and updated with a fresh pack of drivers... also I just upgraded to Windows 10 so I needed an update anyway!

 

After that, I entered the Catalyst Control Center and enabled CrossFireX. Now, when I try to enter GTA V, it only shows 4 GB of memory (as opposed to 6). Is this an issue with the game or am I missing something? In addition, what else should I do to complete this configuration? Thanks!

 

 

Also, one thing worth noting... I have 2 monitors, 1 DVI and 1 HDMI, both connected to the Sapphire. Thanks again! Enjoy Windows 10 :-)

 

[Swndlr]

Memory doesnt stack, I didnt even think you could XFire 2 and 4GB cards

[Emanuel_M]

Like @Swndlr said, memory does not stack. And your system will use the card that has the most memory first. But both of the GPU's cores are working.

[the4thgengamer]

Memory doesnt stack, I didnt even think you could XFire 2 and 4GB cards

Good point! I thought that for a while too. As it turns out, AMD is very lenient with what you can CrossFire. Funny enough, I actually learned this from a Techquickie. Thanks Linus!

 

Source -

[the4thgengamer]

Like @Swndlr said, memory does not stack. And your system will use the card that has the most memory first. But both of the GPU's cores are working.

Thanks for the reply! I can see that now. Now I'm left wondering why GTA is running very slow... settings are not maxed... hm

[Silverer]

Thanks for the reply! I can see that now. Now I'm left wondering why GTA is running very slow... settings are not maxed... hm

Because until DX 12 is supported you only have 2gb of vram...

[Diceair]

omw. Why buy a 2gb and then a 4gb card. in your example you have basically 2x 2gb cards as it will use the card with the lowest memory so the extra 2gb on the 4gb card will go away. in normal crossfire 2gb + 4gb = 2gb or 2gb + 2gb = 2gb. Only in DX12 when they use "split frame rendering" will it use all memory from both cards AKA vram stacking, 

 

GTA 5 will show you the ram from both cards combined so in your example 2gb+4gb (throw 2gb away due to other card bbeing 2gb) = 4GB. So if you still can I will suggest returning the 2gb card or 4gb card and get cards with same memory amount.

[the4thgengamer]

omw. Why buy a 2gb and then a 4gb card. in your example you have basically 2x 2gb cards as it will use the card with the lowest memory so the extra 2gb on the 4gb card will go away. in normal crossfire 2gb + 4gb = 2gb or 2gb + 2gb = 2gb. Only in DX12 when they use "split frame rendering" will it use all memory from both cards AKA vram stacking, 

 

GTA 5 will show you the ram from both cards combined so in your example 2gb+4gb (throw 2gb away due to other card bbeing 2gb) = 4GB. So if you still can I will suggest returning the 2gb card or 4gb card and get cards with same memory amount.

Appreciate the response. I actually had an R9 270X that broke, so I RMA'd it, but I didn't want to go without a card. So I bought the 4 GB card, and would just keep the returned card as a backup. Then MSI asked if they could swap my 270X for a 380 and i was like HELL YEA!

 

So now that I have 2 VERY similar cards, how could I not crossfire them? Hopefully that makes sense! Thanks again.

[-rascal-]

nVidia used to be lenient, where you can SLi two similar GPU's with different amounts of VRAM, but had recently changed the policy for SLi -- via software limitation. There reason was to simply prevent people from running into a situation exactly like your 4GB and 2GB situation.

 

Regardless, Crossfire will still function, but your usage VRAM is limited to whatever the lowest common denominator; in your situation, 2GB.

VRAM does not stack (you mentioned 6GB) because the data the GPU's received is mirrored onto both cards -- each graphics card gets an exact "photocopy" of the data.

 

Going back to the 4GB and 2GB situation. As mentioned about, the data is mirrored. This is why you are limited to your lowest denominator of VRAM. You can't take in 4GB of data when you only have a 2GB capacity. You can't break it down into 2GB + 2GB as that may lead to compute complications.

 

On another note, your two graphics cards in Crossfire does not need to run at matched frequencies for the Core and Memory Clock -- you have a choice to run them independently, or in synchronisation. By default, even in AMD's very own Catalyst drivers, the two card run at independent speeds.

 

If your turn synchronisation on, the Core and Memory frequencies of the primary card (usually the GPU in the top-most PCI-E slot) will be the card used as the reference.

 

Sapphire's TriXX software has the option to turn synchronisation on or off:

Spoiler

You can also see, my two HD 7970's are running a different speeds.

One is operating at 1050MHz / 1500MHz.

The second is operating at 925MHz / 1375MHz.

[the4thgengamer]

nVidia used to be lenient, where you can SLi two similar GPU's with different amounts of VRAM, but had recently changed the policy for SLi -- via software limitation. There reason was to simply prevent people from running into a situation exactly like your 4GB and 2GB situation.

 

Regardless, Crossfire will still function, but your usage VRAM is limited to whatever the lowest common denominator; in your situation, 2GB.

VRAM does not stack (you mentioned 6GB) because the data the GPU's received is mirrored onto both cards -- each graphics card gets an exact "photocopy" of the data.

 

Going back to the 4GB and 2GB situation. As mentioned about, the data is mirrored. This is why you are limited to your lowest denominator of VRAM. You can't take in 4GB of data when you only have a 2GB capacity. You can't break it down into 2GB + 2GB as that may lead to compute complications.

 

On another note, your two graphics cards in Crossfire does not need to run at matched frequencies for the Core and Memory Clock -- you have a choice to run them independently, or in synchronisation. By default, even in AMD's very own Catalyst drivers, the two card run at independent speeds.

 

If your turn synchronisation on, the Core and Memory frequencies of the primary card (usually the GPU in the top-most PCI-E slot) will be the card used as the reference.

 

Sapphire's TriXX software has the option to turn synchronisation on or off:

Spoiler

You can also see, my two HD 7970's are running a different speeds.

One is operating at 1050MHz / 1500MHz.

The second is operating at 925MHz / 1375MHz.

Thank you! I'll take a good look at that software!