I've been tossing around this issue for quite some time as well. The first thing to look at is the motherboard, I use an Asus 880G motherboard (with integrated graphics) with 4G of RAM, it will dynamically manage the memory and prioritize the use of RAM that the XP system doesn't recognize for video memory, if you force the use of 0.75G of RAM that the system doesn't recognize, you'll get a blue screen of death and you'll get more than you bargained for.
If you want to release it:
1. Turn on the system's Physical Address Extension (i.e. PAE).
2. Determine if the motherboard will automatically recall unrecognized memory (critical). there is an option in the BIOS: Above 4g / Below 4g will also have an effect.
3. Click on 'Use unrecognized memory' in ramdisk plus.
Recommended information (including extended reading later):
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