PAE Boot.ini Switch for DEP or 4GB+ memory

This article summarises research into the PAE switch generally used on servers running Advanced Server/Enterprise Editions of Windows with more than 4GB of memory. It includes a brief summary of the uses of PAE and supported Operating Systems.

The Physical Address Extension capability of Windows is:

• Used to provide access on 32-bit Intel systems to greater than 4GB of memory, and is not supported on 64-bit systems
• Not supported on standard editions of Windows 2000
• Supported on standard and enterprise editions of Windows 2003, but not recommended for production use
• Used by adding the PAE switch to the boot.ini and is not required if DEP is enabled through boot.ini with the /noexecute switch, as the OS will assume PAE
• Used by adding the PAE switch to the boot.ini and is not required if hardware-enforced DEP is enabled, as the OS will assume PAE
• Only supported by 32-bit PCI adapters that use Dual Address Cycle (DAC) to transfer 64-bit addresses. Any incompatible adapters will cause driver problems on a server with PAE enabled
• Also used on servers with a total of 4GB, as the total 4GB will not be addressable in user mode unless PAE is enabled.

Anyone considering enabling PAE on a Windows Server 2003 Standard Edition server should be wary. This is not recommended best practise by Microsoft, and both they and any application vendors may be unable to provide support if PAE is enabled.

Excerpt from 291988 referenced below:

• IMPORTANT These configurations are not supported on Windows 2000 Professional and Windows 2000 Server. These configurations are only made available for testing purposes. Do not use these switches in a production environment unless you are using one of the products in the bulleted list at the top of this section.
  
  In these products, the 4 GB RAM Tuning feature enables a 3 GB area of user-mode memory for programs to use. This feature can expand the virtual address range for user-mode memory from 0x0000000 through 0xBFFFFFF (the user-mode address range is typically from 0x0000000 through 0x7FFFFFFF). The range of memory that is available for kernel-mode components shrinks from 0x80000000-0xFFFFFFFF to 0xC0000000-0xFFFFFFFF. We do not recommend using this feature in Windows Server 2003, Standard Edition in a production environment.
  

References:
Physical Address Extension - PAE Memory and Windows

http://www.microsoft.com/whdc/system/platform/server/PAE/PAEdrv.mspx

Operating Systems and PAE Support

http://www.microsoft.com/whdc/system/platform/server/PAE/pae_os.mspx

The amount of RAM reported by the System Properties dialog box and the System Information tool is less than you
expect after you install Windows XP Service Pack 2

http://support.microsoft.com/?id=888137

A description of the 4 GB RAM Tuning feature and the Physical Address Extension switch

http://support.microsoft.com/kb/291988/

Wayne's World of IT (WWoIT), Copyright 2008 Wayne Martin.