I'm considering upgrading my SLI config from my current 2x 8600 GTS (256Mb) to two 8800 GT holding 1024 Mb each.

As I'm running Vista in its 32-bit Version, I know that addressing the memory of my system altogether is limited to 4 gigs.

Given the symmetric nature of SLI's memory usage, does anyone know whether this upgrade will limit my addressable ram to 2Gb or if my whole 3 gigs in my machine will remain usable?

Thanks,
Andres.

It will limit the amount of address space for system ram - thats for definite.

The only part I'm not sure of is this - as its SLI, does it address both 1024 frame buffers, or just the main card? (as only the main cards ram is used for output, but the second cards memory is probably used for its own calculations).

You may be limiting the address space to 2Gb, just with the GFX cards. Probably leaving you to addess only 1.5~GiB or so of RAM.

Do you really need the 1GiB versions?

If you really need the 1GiB versions, you should consider upgrading to a 64-bit OS

Andres said:

Your system memory will be affected. A 32-bit OS can only theoretically address 4GB of memory, PCI cards, the BIOS, Graphics Cards all have memory and need to their memory addressed as well. This goes into what is called the PCI memory address range, the size of this range will vary depending on how much memory needs to be set aside for all the systems components. You really should consider upgrading to a 64-bit OS. If you decide to upgrade you should be able to get an OEM copy of the 64-bit version of windows of your choice relatively cheaply with the purchase of your new graphics card.

Thanks for all your answers,

I'll probably go for Vista 64-bit, as with my company's Enterprise maintenance contract with MS, I can get it for free anyway . I'll just have to make sure the rest of my hardware is supported first.

UPDATE:
Finally went for 2x 8800 GTX 768Mb, they can be found at a pretty cool price. I'm still running Vista 32-bit and all 3 Gigs of RAM are available to the system. This would lead to the conclusion that in SLI, the Graphic card's memory is mapped only once for both cards in parallel.

I'll have to disable SLI to verify this theory, but meanwhile, I'm just happy not having to reinstall

BTW: Perfomance with those cards is pretty neat