There is nothing in Windows itself that limits 32bit Windows from using 4GB
of memory. What limits Windows on modern hardware is the BIOS reserving
memory space for devices. It is called memory-mapped IO and provides a very
rapid but unprotected way of writing data to video cards, etc. The BIOS
reserves the memory space to protect it from the user programs from also
writing there. The whole idea is to get the fastest performace possible out
of things like video cards because that is what users want.

"churin" <churin@new.postalias> wrote in message
news:ulG0LUrxIHA.3680@TK2MSFTNGP05.phx.gbl...[color=blue]
> Ken Blake, MVP wrote:[color=green]
>> On Wed, 4 Jun 2008 21:40:57 +0100, "Doug" <Doug
>> <dougti@discussions.microsoft.com> wrote:
>>[color=darkred]
>>>> How can I check to see if 4GB is being made available for the system to
>>>> utilize?
>>> It sounds like the RAM isn't being detected. What does the BIOS show?[/color]
>>
>>[color=darkred]
>>> Either way, the maximum amount of RAM you will be able to access
>>> (without enabling PAE) is 3.2GB.[/color]
>>
>>
>> Two points:
>>
>> 1. PAE doesn't help on Windows client operating systems, just on
>> servers.
>>
>> 2. The maximum accessible amount is not precisely 3.2GB, but varies
>> from as little as 2 to 2.5 (in rare cases) to as much as 3.5GB,
>> depending on your hardware configuration. Here's my standard post on
>> this subject:
>>
>> All 32-bit versions of Windows (not just XP) 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 is not
>> available to the operating system and applications. The amount you can
>> use varies, depending on what hardware you have installed, but can
>> range from as little as 2GB to as much as 3.5GB. It's 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.[/color]
> Does the above mean as follows?
>
> BIOS and System|Properties show correct size of installed RAM while System
> Tools|System Information and Task Manager|Performance show the maximum
> usable part of the installed RAM. The maximum usable part could be as low
> as 2GB. Therefor,if 4GB is installed and Task Manager|Performance
> indicates that the Total Physical Memory is 2GB, then half of the
> installed RAM is waisted.[/color]