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64 Bit as 32 will only be able to use around 3.6GB of that 12GB RAM.
Yep, as it has been said, a 32 bits OS cannot "see" and use RAM over 3.6GB. In the world of today, 64 bits versions should always be used over their 32 counterparts except for some special cases (some audio editing tools and VST's on Windows have troubles to work in certain 64 bits environments. For example, ReWire with Sonar 64 bits, etc... ).