2 gig Memory boundary

Hi,
Can someone explained or point me to some place where I can understand the 2
Gig RAM baundary in Windows XP?
My understanding is that it is a 2Gig boundary per application. So if I have
an XP machine (Professional) with 2Gigs, and the task manager shows that I am
using up to 1.8 Gig. Does this number reflect the overall usage of memory?
including the OS memory usage?
I would like to put more memory in the machine; nonetheless, I hear that
Windows XP has a 4gig limitation? Is this correct?
Thank you,

"Lamborghini" <Lamborghini@discussions.microsoft.com> wrote in message
news:746EF467-16A8-4C9F-A494-6917F88FB368@microsoft.com...
> Hi,
> Can someone explained or point me to some place where I can understand the
> 2
> Gig RAM baundary in Windows XP?
> My understanding is that it is a 2Gig boundary per application. So if I
> have
> an XP machine (Professional) with 2Gigs, and the task manager shows that I
> am
> using up to 1.8 Gig. Does this number reflect the overall usage of memory?
> including the OS memory usage?
> I would like to put more memory in the machine; nonetheless, I hear that
> Windows XP has a 4gig limitation? Is this correct?
> Thank you,

Back to basics once again...
The virtual address space of XP is 4GB. Since the OS must be mapped into
the address space of every process, some part of the 4GB is not available
to the programs. It is customary to divide the 4GB virtual address space
into 2GB for the OS and 2 GB for the programs.

What you see in the task manager is the amount of virtual address space that
a program is using. It does not reflect what the OS is using.

Now, as for physical memory, you can install up to 4GB to a machine with 32
address lines. However, not all of that 4GB is available because
XP uses memory mapped IO. XP will not use physical memory which overlays
the IO controllers.

Jim