|Most P4 processors can access up to 32GB of RAM but this will be limited by both the hardware and OS installed. All Microsoft client systems limit RAM to a maximum of 4GB (sometimes less) but because of hardware constraints you wont be able to access all of that. In most cases it is the motherboard and BIOS combination that limits the amount and type of memory you can use.|
64 bit systems can access far more memory. Some editions of Server 2008 can access up to 2048 GB of RAM, assuming you can find hardware that can hold that much. In the future that will rise even further.