Tuesday, August 9, 2011

Using 4GB on 32 bits Windows systems (for noobs)

Probably you already know that Windows 32 bits will use only (about) 3 GB of RAM even if you have more than that installed in your computer.

PAE (Physical Address Extension) allows you to enable your computer to use up to 4GB of RAM. So, all your have to do is to enable PAE on your system. Note that PAE is automatically enabled if:
  • your server has hot-add memory ability (ability to add more memory without shutting down the server !!)
  • data execution prevention (DEP) is enabled
If the computer does not support hardware-enabled DEP or is not configured for hot-add memory devices in memory ranges beyond 4 GB, PAE must be explicitly enabled.

To enable PAE:

Windows Vista/Windows 7

Use the following BCDEdit /set command to set the pae boot entry option:

bcdedit /set [{ID}] pae ForceEnable

IF DEP is enabled, PAE cannot be disabled. Use the following BCDEdit /set commands to disable both DEP and PAE:
bcdedit /set [{ID}] nx AlwaysOff
bcdedit /set [{ID}] pae ForceDisable
Note that under Windows 7, PAE should be enabled by default - but there could be also cases when it isn't. So, better enable it manually - "just in case".

Windows Server 2003 and Windows XP/2000

To enable PAE, use the /PAE switch in the Boot.ini file. To disable PAE, use the /NOPAE switch. To disable DEP, use the /EXECUTE switch.


I did some investigations to see if there is any way to clearly see if PAE is enabled or not. It seems there is no way to do it.

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