I disabled every single thing I could on Vista and I couldn't get it below 500mb of RAM. Interestingly though another time when I wasn't disabling anything (such as DWM etc, superfetch was off both times though) it was around the 475mb mark, which is roughly what I think Vista uses when it's doing absolutely nothing (read it a long time ago, it was four hundred and something). The computer's always been on power save yet it still drains a lot quicker compared to say XP (1.5 - 2x)
Comparing say 200mb on XP idle with 400 or so Vista idle it doesn't seem like much of a problem. But as soon as you start doing something with Vista (let's say opening Firefox) suddenly everything doubles (or triples), explorer starts using 50-100mb and sometimes even more some crazy reasons (not as often now since SP1...) and it jumps back up to 700-1000mb of ram again - and Firefox hasn't even loaded yet - it's still initializing and the process is only using 6mb so far...crazy! Sure other things like system-resources-that-do-stuff-that-can't-be-seen-without-other-useful-programs are contributing to the spike in ram, but it's still a massive leap just by doing one simple task (I guess that's where the limiting how much ram the OS can use would come into play
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