The Physical Memory Limits of Windows Vista/Xp 32bits

Clarification

There is no support for a full 4GB of Memory in Windows according to Mark Russinovich's Blog
After some research a simple explanation is that although originally PAE (Physical Addressing Extensions) was implemented to support more than 4GB of Memory Address, due to poor driver programming by vendors has resulted in Microsoft's convenient decision to simply pull the plug on PAE support in Client OS.
Their rationale being they couldn't resolve crashes on Windows 32bit Client Machines due to poorly programmed device drivers like WebCam etc.
However, this is not to say you cannot enable PAE on any 32bit Windows Operating System.
However it is not ANY Windows Operating System

Physical Memory Limits: Windows Server 2008

The following table specifies the limits on physical memory for Windows Server 2008. Limits greater than 4 GB for 32-bit Windows assume that PAE is enabled.

Version	Limit in 32-bit Windows
Windows Server 2008 Datacenter (full installation)	64 GB
Windows Server 2008 Datacenter (Server Core installation)	64 GB
Windows Server 2008 Enterprise	64 GB

Physical Memory Limits: Windows Server 2003

The following table specifies the limits on physical memory for Windows Server 2003. Limits over 4 GB for 32-bit Windows assume that PAE is enabled.

Version	Limit in 32-bit Windows
Windows Server 2003 with Service Pack 2 (SP2), Datacenter Edition	128 GB 64 GB with 4GT
Windows Server 2003 with Service Pack 2 (SP2), Enterprise Edition	64 GB
Windows Storage Server 2003, Enterprise Edition	8 GB
Windows Server 2003 R2 Datacenter Edition Windows Server 2003 with Service Pack 1 (SP1), Datacenter Edition	128 GB 16 GB with 4GT
Windows Server 2003 R2 Enterprise Edition Windows Server 2003 with Service Pack 1 (SP1), Enterprise Edition	64 GB 16 GB with 4GT
Windows Server 2003, Datacenter Edition	128 GB 16 GB with 4GT
Windows Server 2003, Enterprise Edition	32 GB 16 GB with 4GT

Physical Memory Limits: Windows 2000

The following table specifies the limits on physical memory for Windows 2000.

Version	Limit in 32-bit Windows
Windows 2000 Advanced Server	8 GB
Windows 2000 Datacenter Server	32 GB

As you can see they are all Server OS which makes me wonder, since most in fact all Drivers are certified by Microsoft, shouldn't they work with PAE? Or is it that they don't want to ?

It turns out that the reason Windows Vista/Xp 32bit "eats" up your RAM is because all hardware require memory address to map location.
Xp/Vista 32bit addresses do not exceed 4GB because Microsoft removed this functionality hence

Amount Of Space Left = Available 4GB address - Addresses Taken Up By Device Hardware

This number varies from System to System hence there is 2 ways of overcoming this issue

1. Get a 64bit Windows OS
2. Get a 32bit Windows Server OS listed above

If you are a student with Microsoft Academic Alliance in your institution you are in luck, as you can get the software free

Take a look here and here

Sorry again if my previous post caused some confusion