I keep hearing that if you get, let's say 590 GTX 3GB, then you will really have 1.5GB of RAM, instead of advertised 3GB. Is it true or just a misleading information? My guess right now, is that it's BS... Why would both Nvidia and AMD advertised it that way? 6990. 590. 690 etc. must have what they got written on their boxes.
Also, there are same rumors about SLI/CFX configurations, so if you get 2x580 GTX 3GB each, then in the end you will still have 3GB, not 6GB. Really?
The technically have 3GB's of v-ram on the dual GPU cards, however, given that both GPU's on each card must have the same information loaded in vram for their own rendering, they behave like they have half the advertised amount.
It will be bottlenecked. The data is mirrored between the two cards because they are each spitting out alternate frames therefore they need identical data in each set of VRAM feeding each GPU. I didn't know that either when I bought my old 9800 GX2. 500mb of RAM was a hard reality.
Mirroring was a conscious design decision when developing the technology. It allows the GPUs to render alternating frames, which greatly simplifies what the driver vendors need to do to support applications. If it were not done that way, the application or driver would have to dictate which particular objects were rendered on which GPU. In addition, techniques like Z-culling would be difficult if one GPU didn't know what the other was rendering, especially if they rendered overlapping objects (which nearly all objects in games are).
Well, not really. You have two GPU's (and sets of RAM) running at a set clock rate, so it's not really doubled. You have two GPU's running at say, 900 mhz, not one card running at 1800 mhz. Close, but not exactly the same thing in my eyes.
The GPU performance would theoretically be doubled (usually it works out slightly less than double the performance). The memory interface and bandwidth would not be doubled since each one is only connected to one GPU.
A dual GPU card is the same as two single GPU cards in almost all respects. Because it does have the same vram on both cards, they can put the total value of vram. You just have to realize it's like two cards with half the vram on each card.
I agree. Like I said, I bought a 9800 GX2 thinking I was getting a 1GB card. In a roundabout way your are.. And that's how they can get away with it. But oh well, I learned my lesson. At least you asked beforehand.
Sheer brute force. You have two GPU's firing off alternate frames, so if you're running at 60 fps say, each GPU is running at 30 fps. If you had one GPU, it would have to fire all 60 fps off by itself to give the same performance.
Ok, but then shouldn't SLI/CFX mode exactly double FPS you were getting on a single GPU? I know some SLI/CFX configs perform about 70% faster than a single setup, why it is not doubling performance 2x then?