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View Full Version : SLI does not double your ram. Right?


Pixelsmack
03-22-07, 05:12 PM
This guys article is a little in error. (on nvews front page)

http://www.tweaktown.com/articles/1068/9/page_9_final_thoughts/index.html

Unless something has changed, SLI mode does not give you a 1024mb texture bank using two 512mb cards. Each GPU still only gets it's on board ram to load and swap textures to.

This guys review seems to try and make a point that the combined ram is helpful. It's not, his own benchmarks even show that fact it would seem. When he test at XHD res on texture heavy games the difference in performance is astronomical.

Seeing that the two SLI cards setup for testing were rather close in every test (proving it's more a function of the combined GPU power in which this case the two cards are similar in specs) but then fell off from each other greatly in the XHD and large texture ram game tests shows that the larger per card ram makes a difference.

Otherwise they both should have maintained consistent performance. As no game really uses 1.2GB of texture ram effectively. Most barely scratch the 640mb area. The ones he tested anyway.

J-Mag
03-22-07, 05:18 PM
Another reason why I don't really care about the conclusions reviewers come to. I see this kind of thing regularly where the data says something different than the reviewer.

Dazz
03-22-07, 06:32 PM
Thats right which is why when they sell the 7950GX2 cards it's miss leading as they lable the cards as 1024MB or 1GB but only 512MB can ever be used.

T.h.o.m.a.s.
03-22-07, 06:59 PM
but if one card renders upper half and the other card the lower half,
then would they have to load the same textures ??

SlieTheSecond
03-22-07, 07:15 PM
The ram on both cards have to contain identical information.

Rakeesh
03-22-07, 07:16 PM
I remember SLI on 3dfx cards would combine memory.

J-Mag
03-22-07, 07:20 PM
but if one card renders upper half and the other card the lower half,
then would they have to load the same textures ??

Rarely does any game run in SFR anymore, most use AFR where each card renders the whole frame (alternatingly of course). Even the games that use SFR still need to load the same textures in each buffer because of several reasons: Many textures will be used in both halves, Angle Of View is not Constant, Forward Motion will bring textures into the other half of the screen, etc...

Dr.Nick
03-22-07, 07:25 PM
nVidia definitely "enhanced" the 7950GX2 specs a little to pull attention. They list it as a 512bit, 1GB ram, with over 75GB/s of bandwidth hehe. It's not a lie by any means but it also isn't 100% true. Does that make sense? lol
As for your question, each GPU can only access its own 512mb buffer and SlieTheSecond is also correct.

T.h.o.m.a.s.
03-23-07, 05:49 AM
Rarely does any game run in SFR anymore, most use AFR where each card renders the whole frame (alternatingly of course). Even the games that use SFR still need to load the same textures in each buffer because of several reasons: Many textures will be used in both halves, Angle Of View is not Constant, Forward Motion will bring textures into the other half of the screen, etc...

thanks man i didn't knew that:afro2:

stevemedes
03-23-07, 02:24 PM
Maybe SLI 2.0 will make it possible to combine the RAM on both cards. That'd be fetchin sweet.

Dazz
03-23-07, 02:50 PM
nVidia definitely "enhanced" the 7950GX2 specs a little to pull attention. They list it as a 512bit, 1GB ram, with over 75GB/s of bandwidth hehe. It's not a lie by any means but it also isn't 100% true. Does that make sense? lol
As for your question, each GPU can only access its own 512mb buffer and SlieTheSecond is also correct.
Thats why i stated it's miss-leading. Although it does indeed have 1GB ram only 512MB can ever be used.