Quote Originally Posted by sledger View Post
Apparently quite an important factor is if you have a graphics card with (for example) 1GB RAM (or SLi with 2GB total) as it becomes part of the 4GB limiting equation which for 32bit 'gamers' PC's is quite serious.
This conflates two subtly different issues. Like you say, the graphics card memory uses part of the system's total address space, which is much more of an issue on 32bit machines than 64bit machines.

The flag which this post is talking about setting allows Windows to change the way virtual address space is arranged for 32-bit applications rather than for the system as a whole - by default they only get 2G of address space, with this flag set they may get 3G or 4G.

Even on a 64-bit machine with umpteen G of memory, a 32-bit application will normally only get 2G of address space (and it would still get this 2G space even if the machine had 1G of physical RAM).