GTX 690 2gb of vram or 4gb total? 7990 3gb or 6gb total?

[Caenlen29]

reason I ask is:

http://youtu.be/4zYGR4R7Svk?t=2m50s


this guy is saying u get all the memory to use, where as most people say no the gtx 690 is still only 2gb, its same as 2x gtx 680 in sli, but this guy is saying no, u get the full 4gb...


so which is it? can someone clarify?

 

[MxPhenom 216]

The guy in the video doesn't know what he is talking about. GTX690 is 2GB of usable VRAM and the 7990 is 3GB of usable. Same thing with normal SLI or crossfire with separate cards. VRAM does not add up.

 

[Maban]

You get to use it all, but it's mirrored. So effectively it's just 2GB for the 690 and 3GB for the 7990.

 

[15th Warlock]

An analogy would be a twin engine (GPU) aircraft with an independent 500 gallon fuel tank (VRAM) on each wing, each engine can access the fuel on its respective tank, but not the fuel from the tank on the opposing wing.

Yes, your airplane effectively carries a total of 1000 gals. of fuel on board, but each engine can only access 500 gals. at a given time.

 

[Caenlen29]

An analogy would be a twin engine (GPU) aircraft with an independent 500 gallon fuel tank (VRAM) on each wing, each engine can access the fuel on its respective tank, but not the fuel from the tank on the opposing wing.

Yes, your airplane effectively carries a total of 1000 gals. of fuel on board, but each engine can only access 500 gals. at a given time.

So if Skyrim uses say 2400 mb of vram on a single 7970, would it be limited by using a GTX 690 or it would it still be able to use that much vram?

 

[xxdozer322]

^its a dual gpu (like SLI) both have access to the 2gbs of ram...With that said, one gpu is used for the top portion of your monitor, while the other doing work for the bottom half

 

[MxPhenom 216]

^its a dual gpu (like SLI) both have access to the 2gbs of ram...With that said, one gpu is used for the top portion of your monitor, while the other doing work for the bottom half

What in the world did you just say?

 

[Maban]

The SLI FAQ doesn't go into much detail about it but it does say the following:

When I configure two graphics cards in SLI mode, do the graphics cards work together to create double the memory size?

No. In SLI mode, each graphics card uses its own frame buffer memory to render a 3D application. The operating system will report a graphics card frame buffer memory size that is found on a single graphics board.

 

[xxdozer322]

What in the world did you just say?

free post? sounded right, but i guess after running 8 miles and having a beer, anything sounds right

 

[MxPhenom 216]

free post? sounded right, but i guess after running 8 miles and having a beer, anything sounds right

Okay, because multi GPU setups do not work like that at all. The screen is not split up. The GPUs just alternate what frame is processed and displayed.

 

[Maban]

Split Frame Rendering mode has one card do the top half and the other do the bottom half.

 

[xxdozer322]

I guess it was just the "easiest" way of getting the point across. Ive never had SLI, but from what ive read here on the forums, it was the easiest way to explain. Noob to Noob, sort to say, please forgive me

 

[Caenlen29]

So if Skyrim uses say 2400 mb of vram on a single 7970, would it be limited by using a GTX 690 or it would it still be able to use that much vram?

No one has answered my question...

 

[Maban]

When I was running my two 470's in SLI, I had set Skyrim to max settings and then some. It very much slow down, practically froze, when it tried to use more than 1280MB of video RAM.

 

[15th Warlock]

No one has answered my question...

It would be limited by the VRAM available to each GPU, so yes, it would stutter like crazy

 

[Xaser04]

So if Skyrim uses say 2400 mb of vram on a single 7970, would it be limited by using a GTX 690 or it would it still be able to use that much vram?

Depends if Skyrim is actually using 2.4GB of VRAM or just reporting that it is.

If it actually is using 2.4GB of VRAM a GTX690 will be a stuttery mess.

 

[EpicShweetness]

Wait a minute, if the data is mirror, but the GPU's render different frame's how the hell does that work! It's illogical, I think I understand a bit better from programming a few RAID arrays.
Ok so think about it like this
GPU 1 GPU 2
Data:
A
B
C
D
E
F

The work is then split up according to frame rendering.
GPU 1: A, C, E
GPU 2: B, D, F

That would explain why your frame buffer is still 2GB, but 4GB overall. I wouldn't be surprised if a single frame buffer gets bogged down easier than a monolithic one. There is a certain amount of mirrored data.

 

[radrok]

Take the GTX 690 as two GTX 680 on one single PCB.

They basically divide the PCB in two parts which are connected by a PLX bridge instead of a SLI bridge that would be used on two separate cards.

The way two GPUs communicate on the GTX 690 is just slightly different than two separate GTX 680.

Differences being a frame metering device and a PLX chip instead of a SLI bridge.

IN NO WAY one GPU in the GTX 690 can access the other GPU's memory.