I have a computer with 3 Gb of RAM. Its a nForce 630i based system, with integrated Geforce 7100 video, plus an addon PCIe Geforce GT520 graphics card, with 1 GB dedicated memory. With Windows 7 x86 32 bits the amount of available memory is equal to the installed memory, 3072 Mb, deducting the memory asigned to the integrated video card, which is just 64 Mb, the minimum allowed by the mobo's BIOS. But when I installed Windows 8 x86 32 bits I found out that somehow the hardware reserved memory grew up to 1 GB, so now I only have a maximum amount of 2048 Mb of available memory. Any clue why this happens? I didnt change anything in the settings before installing, I just formatted the system partition and installed 8 cleanly. After finding this problem I tried changing all available BIOS settings, disabling onboard video, changing the memory asigned to the integrated card, changing the order of video enumeration, etc. Any clue why Windows 8 needs to reserve much more memory than 7 for the same configuration? Note I'm talking about 32 bits, x86 versions, this got nothing to do with the 64 vs 32 bits I think, as I dont have anything close to 4 Gb of memory, not even 3,27 Gb, just 3072 Mb or RAM.
IGP drivers can occasionally botch your memory configuration so you can try resetting with a different size of reserved video memory and then reinstalling the latest video drivers (for both your IGP and video card). Also make sure you have the latest chipset driver(s) installed before tooling with video and memory. But, I've read that Windows 8 32-bit edition's MMIO can be even less forgiving then Windows 7. You can try dorking around with your BIOS settings to see if you can get the OS to detect and prevent it from disabling RAM, but the only sure way is to install the 64-bit version of the OS.