From the TFA:
"Various devices in a typical computer require memory-mapped access. This is known as memory-mapped I/O. For the MMIO space to be available to 32-bit operating systems, the MMIO space must reside within the first 4 GB of address space.
For example, you have a 8800GTS 640Mb Graphics card. That cards memory MUST be mapped withing the first 4Gb of address space. If you have 4Gb of memory installed then part of the addresses are reserved for the graphics card memory map. The graphics card memory now OVERWRITES a part of the system memory. 4Gb = 4096Mb - 640Mb = 3456Mb. If you have 2 GTS 640Mb then the amount of TOTAL RAM available to the O.S. becomes even less and so on. The amount system memory is reduced is all dependent on the amount of devices installed in the system. However, to avoid potential driver compatibility issues, the 32-bit versions of Windows XP/Vista limit the total available memory to 3.12 GB."
So i'm wondering if linux users are running into this same issue were they've got 4GB of RAM installed but are only seeing a little more than a 2? Or are you guys seeing the full amount?