I am currentlu running Vista Ultimate SP1 with 4GB of RAM with Intel Q6600
quad CPU. I have read that the 32 bit version (which I'm running) can only
see about 3GB ...
Yes. All 32-bit versions of Windows (not just Vista) have a 4GB
address space. That's the theoretical upper limit beyond which you can
not go.
But you can't use the entire 4GB of address space. Even though you
have a 4GB address space, you can only use *around* 3.1GB of RAM.
That's because some of that space is used by hardware and not
available to the operating system and applications. The amount you can
use varies, depending on what hardware you have installed, but is
usually around 3.1GB.
Note that the hardware is using the address *space*, not the actual
RAM itself. The rest of the RAM goes unused because there is no
address space to map it too.
... although it reports 4GB.
Yes, since SP1. I think this was a very poor change, since people are
not misled into believing that Vista is seeing and using all 4GB,
where in reality it's the same amount it always was--around 3.1GB.
Is there any reason why I should not consider moving to the 64 bit version?
Yes.
1. There may not be 64-bit drivers available for all your hardware, so
you might need to replace your printer, scanner, etc
2. A 64-bit operating system is faster than a 32-bit one if you also
run 64-bit applications. With 32-bit applications, you will probably
notice little or no difference in speed.
Why do thing you need more RAM than 3GB? How much RAM you need for
good performance is *not* a one-size-fits-all situation. You get good
performance if the amount of RAM you have keeps you from using the
page file, and that depends on what apps you run. Most people running
a typical range of business applications under Vista find that
somewhere around 2GB works well, although for others 3GB might be
better. Unless you are doing things like editing large photographic
images or videos, you will probably see no benefit by having access to
more than 3GB.
If you are currently using the page file significantly, more memory
will decrease or eliminate that usage, and improve your performance.
If you are not using the page file significantly, more memory will do
nothing for you.