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How is video ram affected in SLI/Crossfire cards?

post #1 of 10
Thread Starter 
This is for all you geniuses out there. I understand that in crossfire and SLI that 2 cards don't double the overall VRAM, therefore two 3 GB cards doesn't mean you have 6 GB dedicated. However, the cards do work in mirror of eachother, meaning that it should actually utilize all of the VRAM. So here's the real question: If I wanted to play on a 4k monitor (which would need a LOT of VRAM and we will assume that one 3 GB card will be bottle-necked ONLY because of the VRAM), assuming that the 7950 is actually fast enough to run a 4k monitor at full FPS, but can only run it at 30 FPS because it's bottle-necked only because of VRAM... Would adding another 7950 in crossfire actually increase performance from a VRAM standpoint? Meaning it would use all 6 GB of ram or would it only use 3 GB and still be bottle-necked ONLY due to VRAM?

I know this is a dumb scenario, but I couldn't find a clear answer on how VRAM works. If you don't understand my stupid question, feel free to tell me and I'll help elaborate thumb.gif .

Thanks again for the help! biggrin.gif

-TJ
post #2 of 10
For bf4 maxed at 5670x1080 the vram usage is 3.1gb probably during 2 or 1 years 3gb vram will be fine for 4k

And if it runs at 30hz with a better card is the hdmi 1.4a which limots to 30hz
post #3 of 10
Thread Starter 
Thanks for the reply... didn't answer my question at all though.
post #4 of 10
Quote:
Originally Posted by TJD269 View Post

Thanks for the reply... didn't answer my question at all though.
What else do you want to know?
post #5 of 10
Quote:
Originally Posted by TJD269 View Post

This is for all you geniuses out there. I understand that in crossfire and SLI that 2 cards don't double the overall VRAM, therefore two 3 GB cards doesn't mean you have 6 GB dedicated. However, the cards do work in mirror of eachother, meaning that it should actually utilize all of the VRAM. So here's the real question: If I wanted to play on a 4k monitor (which would need a LOT of VRAM and we will assume that one 3 GB card will be bottle-necked ONLY because of the VRAM), assuming that the 7950 is actually fast enough to run a 4k monitor at full FPS, but can only run it at 30 FPS because it's bottle-necked only because of VRAM... Would adding another 7950 in crossfire actually increase performance from a VRAM standpoint? Meaning it would use all 6 GB of ram or would it only use 3 GB and still be bottle-necked ONLY due to VRAM?

I know this is a dumb scenario, but I couldn't find a clear answer on how VRAM works. If you don't understand my stupid question, feel free to tell me and I'll help elaborate thumb.gif .

Thanks again for the help! biggrin.gif

-TJ

It wouldn't help.


How it works is the same initial dataset gets copied to each card's memory. Then the each GPU works on a subsection of that dataset and returns it.

So 3GB of effective memory is still 3GB of effective memory with 1, 2, 3, or 4 cards.
Once again...
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post #6 of 10
Thread Starter 
Ahhh ok thank you sir thumb.gif
post #7 of 10
To answer your question 4k is about bandwidth. Essentially you are doubling your vram bandwidth. If the card can handle 4k already you are essentially (well call it a pipe for ease of term) doubling it. Your ram AMOUNT stays the same but you will have double scaling which is what SLI is (Scale-able Link interface). So 4k is basically a much larger resolution, so it can take each cards vram and sort out the pixels at double the rate vs just once and waiting for the card to reach the other part of the resolution. I guess I can go technical but in ease of terms this is what is does. It takes each card and splits up what you have one either one monitor and the other or in 4k's monitor handles horizontal and vertical refresh separately AMD says, By accessing the memory of the GPU through PCIe AMD claims that it can alleviate the bandwidth and sync issues that were causing problems with Eyefinity and tiled 4K displays. nvidia says, 4K resolution is obviously heavier on video memory consumption than lower resolutions. Four times the pixels will mean four times the memory used for screen sized buffers, in addition to any additional memory consumed by higher resolution source art (“Maximize Texture Resolution” above) or higher resolution intermediate surfaces such as shadow maps (“Beware of Magnification Artifacts” above).
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post #8 of 10
Thread Starter 
Quote:
Originally Posted by Jedson3614 View Post

To answer your question 4k is about bandwidth. Essentially you are doubling your vram bandwidth. If the card can handle 4k already you are essentially (well call it a pipe for ease of term) doubling it. Your ram AMOUNT stays the same but you will have double scaling which is what SLI is (Scale-able Link interface). So 4k is basically a much larger resolution, so it can take each cards vram and sort out the pixels at double the rate vs just once and waiting for the card to reach the other part of the resolution. I guess I can go technical but in ease of terms this is what is does. It takes each card and splits up what you have one either one monitor and the other or in 4k's monitor handles horizontal and vertical refresh separately AMD says, By accessing the memory of the GPU through PCIe AMD claims that it can alleviate the bandwidth and sync issues that were causing problems with Eyefinity and tiled 4K displays. nvidia says, 4K resolution is obviously heavier on video memory consumption than lower resolutions. Four times the pixels will mean four times the memory used for screen sized buffers, in addition to any additional memory consumed by higher resolution source art (“Maximize Texture Resolution” above) or higher resolution intermediate surfaces such as shadow maps (“Beware of Magnification Artifacts” above).
So this will make crossfire/SLI better when running when on high resolution and textures, where only 1 card's VRAM isn't enough?
post #9 of 10
Quote:
Originally Posted by TJD269 View Post

So this will make crossfire/SLI better when running when on high resolution and textures, where only 1 card's VRAM isn't enough?
either . 770Gtx2gb sli or a 7870Ghz will ran out of vram at 4k no matter how much crds you use they will run out of vram when a single 780gtx 3gb/hd 7970/280x doesnt
post #10 of 10
Lets be clear here the more vram the better for larger resolutions and as far as settings go cranking them up as wel like to call it, but if hes running low to mid settings he would be fine technically with a 660 ti. http://mygaming.co.za/news/hardware/54663-play-games-at-uhd-4k-resolution-the-hardware-you-need.html. If he want to play at high settings then yes titan 3 way or 780 ti 3 way or even 2 way will work, but to this point its still hard to on some games to set all setting high they are finding even a titan will have not enough at some times.
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