Vista 64 bit if I have 4GB of RAM to use?

[mwhals]

It is the same reason that XP 32 can't see 4 GB. A 32 bit OS can only see 4 GB total. Off the top of this total comes hardware memory. What is left is what you will see in a 32 bit operating system. If you want to see all 4 GB, you need to use the 64 bit version since it can use the 4GB and place the hardware at a higher memory setting than 4 GB.

 

[Nothinman]

So my Windows Vista Ultimate will only see 3GB of the 4GB RAM I have in my machine? I'm running the 32bit version of Vista. If this is the case, why?

Maybe 3G, the value varies depending on your hardware. Please read the thread, it's been explained more than once here.