I'm typing this right now on an XP machine with 4GB installed, although the OS only sees 3.5GB. I admit, however, that I haven't tried to let a single running application access all of it at once, I remember from somewhere someone saying something about how a single app in XP can only use so much memory, although I haven't tested if this is true.
Ah, well, it should be correctly used for u then. U must not forget that there are such things as onboard graphics memory (if urs is not a dedicated graphics card - most common cause for <Max ram issue), pci cards / roms memory usage, and even controllers memory..... all these eat up some memory....
Hence, even with 4GB max installed, u might not have all of them for your pleasure.
And to answer the question on whether its possible for a single application to use 4GB - yes theorectically, but it would be insane. But this is not happening on XP, since max memory "handle-able" by XP is 2^32 = 4294967296b = 4194304kb = 4096MB = 4GB exactly (1GB = 1024MB, 1MB = 1024kb, 1kb = 1024b, b=bytes=8 bits)
Why? Cos XP is a 32bits application. Hence, Vista works more "efficiently" in theory than XP becos of this 64 bit capabilities. Then again, XP needs some about 750MB ram to run (as basic with SP3 and basic antivirus and firewalls), whilst vista requires a whopping close to 1.3GB-1.7GB to run efficiently (with SP and basic apps). So, unless u have 4GB XP vs 8GB Vista, u will hardly say which is better...... (And question is do u really need 64 bits app since most do not support it, drivers support sux and aint we hearing its being 'abandoned' for a new windows OS soon?)
For more on the 4GB thingy, see
this.
Edit - Another Guy, it is NOT a necessary evil. It is an absolutely redundant evil...... that should be eliminated. Lol.
