Firstly, physical ram is different from virtual ram.
Virtual ram "Act" as ram where the computer writes the info. to
somewhere in the computer, and then comes back to it when it needs
it.
For Win XP, etc, 32bits operation system its 4gb at most of virtual
ram.
Physical Ram is the actual ram, where the graphics card can use and
certain operations need. That IS, some programs REQUIRE the use of
actual physical ram where the process of info is stored IN the ram
inside to be DYNAMICALLY retrieved and stored and NOT write
somewhere then read it back.
Ofcourse, when you see it, the virtual ram purpose is LESS useful
and SLOWER than the physical ram. Cuz reading from actual ram is
much much faster than virtual ram.
Also some programs requires large size physical ram to run. Such as
very powerful CADCAM, simulation softwares, animation softwares,
Games, etc, where what THEY NEED IS Physical ram, not virtual ram.
Because the process cannot be "chopped" up into separate sections
to write then read then write then read, but read all the way then
process then write.
Lastly, although 4Gb of virtual ram can be allocated, but microsoft
states that the max it can use is 4Gb of whatever ram.
So, e.g. if you have 512Mb (physical) you can allocate up to 3Gb
512Mb (virtual ram) though you can set up to 4Gb v.ram but they
only used up to 3.5Gb v.ram
likewise, 1gb p.ram ==> max. of 3gb v.ram can be allocated.
