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SLI graphics cards with different amounts of VRAM?

Akagi

Akagi

Akagi

Caporegime
Joined
29 Jul 2011
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In acme's chair.
If I were to buy a 4GB EVGA GTX670 and a pair of 2GB EVGA GTX670's, could I put the three in SLI with the 4GB as the primary card, and have 4GB of VRAM but save money on the other two cards by buying 2GB models?

Only hypothetically of course, I was just wondering if it would work that way.

Same with 3GB/1.5GB GTX580's, 2GB/1GB HD7850's in crossfire etcetera.
 
No

I think it will run but on your 4gb card only 2 gbs would be used

All cards in sli use the same amount of vram.
 
Kaapstad said:
No

I think it will run but on your 4gb card only 2 gbs would be used

All cards in sli use the same amount of vram.
Click to expand...

I thought that with SLI only the VRAM of the top-most card is used? So in a 3x 2GB SLI configuration you would have 2GB of usable VRAM etcetera?
 
You can't mix different vram sizes. The its the clock speed that down clock for instance if you have a stock card and a factory Overclocked card the Overclocked card will slow down to the stock speeds. I also acme is correct iirc
 
You can sli 6xx 4gb with 6xx 2gb but available vram will be 2gb,

Can I mix and match graphics cards with different sizes of memory?

When purchasing a second graphics card, you should try to match the memory size so that you are ensured full value and performance from your purchase. However, while it is not recommended, NVIDIA does offer the flexibility to run graphics cards with different sized memory by using CoolBits. Using CoolBits (value set to 18), you can force both of the cards to use the lower of the two memory sizes and operate them together in SLI mode. When dissimilar memory sizes are enabled to work together using CoolBits, the effective memory size for each card becomes the smaller of the memory sizes.


This was taken from Nvidias website

http://www.geforce.com/hardware/technology/sli/faq#c19
 
Last edited:
So in otherwords its pointless unless you wanna waste that £100 extra for the 4Gb?

Just wondering why do you need tri sli? And if its loads screens why didnt you think of AMD?
 
acme15 said:
I thought that with SLI only the VRAM of the top-most card is used? So in a 3x 2GB SLI configuration you would have 2GB of usable VRAM etcetera?
Click to expand...

Essentially, but to clarify: the vram of all the cards in the SLI configuration is utilised, although only the individual card memory is the 'effective' usable amount (for want of a better word). Each card holds exactly the same data in the vram because each core needs fast access to it. If the data was held on only the primary card then the other cores would suffer increased latency while data is moved from the primary vram to their cache/registers via the SLI bridge or pci-e interface.

Ginger-Menace said:
You can't mix different vram sizes. The its the clock speed that down clock for instance if you have a stock card and a factory Overclocked card the Overclocked card will slow down to the stock speeds. I also acme is correct iirc
Click to expand...

On the 600 series you can run cards in an SLI configuration at different clock speeds.
 
Why buy something different?

1. It looks crap
2. The VRAM may not match and some will be wasted
3. Clock speeds may be different and you may lose performance

You should always put thought into card purchases to ensure you can afford another later ;)

Good luck
 
BaDBoY_uK said:
Why buy something different?

1. It looks crap
2. The VRAM may not match and some will be wasted
3. Clock speeds may be different and you may lose performance

You should always put thought into card purchases to ensure you can afford another later ;)

Good luck
Click to expand...

1. It would not look crap as the EVGA SC GTX670 2GB and 4GB editions look the same minus the backplate included with the 4GB model.

2. I realise that now, it was the reason why I made this thread

3. I knew that already, but I would have matched the clock speeds anyway.

Also I did say that this was only a hypothetical question, it was more to help me spec systems for other people than for myself, as much as I would love three GTX670's I really cannot afford it.
 
acme15 said:
1. It would not look crap as the EVGA SC GTX670 2GB and 4GB editions look the same minus the backplate included with the 4GB model.

2. I realise that now, it was the reason why I made this thread

3. I knew that already, but I would have matched the clock speeds anyway.

Also I did say that this was only a hypothetical question, it was more to help me spec systems for other people than for myself, as much as I would love three GTX670's I really cannot afford it.
Click to expand...

Apologies fellow forum member, I did not mean to criticize. Obviously price comes into it, hence my point. #1 is purely aesthetics. Number 2 is the most important. Why waste VRAM. In fact, give your extra VRAM to me ;)
 
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