Enable PAE in Windows Server 2008

In the last two days I had responded to an AWE related question atleast 4 times. The question revolved around enabling AWE on a server running Windows Server 2008 (32 bit). Even though AWE is enabled in SQL Server, it will not take effect if the Operating System is not configured with the /PAE switch.

Some facts about Physical Address Extension (PAE).

  • By default 32 bit systems will not be able to access more than 4 GB of RAM
  • The PAE feature enables 32 bit systems to recognize more than 4 GB of RAM installed
  • However PAE switch does not increase the Virtual Address Space (VAS) available to the windows process. Any windows process has a VAS size of 4 GB. Again this is divided into User Mode Space and Kernel Mode Space of 2 GB each. The /3GB switch will increase the User Mode space to 3GB there by decreasing the Kernel Mode space to 1 GB

Coming back to the question “Is /PAE switch still available in Windows Server 2008“. The answer is Yes if it is Windows Server 2008 (32 bit). In earlier versions of Windows to enable PAE, c:boot.ini file had to be edited. Against each Operating System listed in boot.ini, the /PAE switch had to be entered. The boot.ini looks like this

[boot loader]
timeout=0
default=multi(0)disk(0)rdisk(0)partition(1)WINNT
[operating systems]
multi(0)disk(0)rdisk(0)partition(1)WINNT=”Microsoft Windows 2003 Enterprise Server” /fastdetect /PAE

After making this change, rebooting the server would ensure that the Server recognizes memory greater than 4 GB.

In  Windows Server 2008, this change cannot be done in boot.ini file. It has to be done using the BCDEDIT /SET command. In order to enable PAE, the following needs to be done.

  1. Open Command Prompt with elevated privileges (Runas Administrator)
  2. Execute the following command
  3. BCDEDIT /SET PAE ForceEnable

PAE will be enabled after the server reboot. To disable PAE  /NOPAE keyword needs to be used instead of PAE in the above command.

2 thoughts on “Enable PAE in Windows Server 2008

  1. karthik

    Hi Pradeep,

    Can you please guide me in understanding about awe. I always get confused about it. Let me know if my understanding about awe is right?

    AWE is not an extension of memory nor it changes the memory structures like PAE or /3GB,but it is a windowing technology that allows a process to access more memory than it VAS. It does this by reserving some space in the VAS of the process and uses that space to map addresses to the physical memory.

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