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15Jul/08Off

Utilising more than 4GB of RAM with Windows Server 2003 Standard Edition – Enabling /PAE /3GB

We recently needed to upgrade one of our applications, and the new version requires an addition server instead of the application and SQL it requires a back end search, a front end web server and a SQL server. The specifications of the new server which are "required" to qualify for support are pretty high. The problem is that the actual processor usage is very light, and it is very hard to justify buying a whole new server that I know is going to be barely used.

The alternative plan was to virtualise the servers, make use of the existing physical hardware, upgrade the RAM and add a couple of drives to the RAID array, which we opted for because it would cost less than £300, instead of £3000.

I forgot, however, the 4GB limitations of Windows Server 2003. 32 bit processors cannot address more than 4GB of RAM, so to get round that you can use Physical Address Extensions (using the /PAE switch in the boot.ini) which enables you to utilise more than the standard 4GB.

Typically a 32 bit system with 4GB RAM will allow 2GB for the kernel, and 2GB for the Applications to use. This means that each application can virtually address up to 2GB of RAM. You can change this balance using the /3GB option in the boot.ini to allow 3GB for applications. Think carefully before doing this!

To enable PAE:

  1. Right click "My Computer", select "Properties"
  2. Select the "Advanced" tab and click the "Startup and Recovery" button
  3. Under "System startup" you can click "Edit" to open the boot.ini file.
  4. BE CAREFUL! You can render you OS unbootable! Add the /PAE and /3GB options to the startup (see below for an example) Save, OK and reboot.

multi(0)disk(0)rdisk(0)partition(2)\WINDOWS="Windows Server 2003, Standard" /PAE /3GB /fastdetect

It's worth noting that if you have DEP (Data Execution Protection) turned on then PAE will be turned on by default. DEP is on automatically in Windows Server 2003 SP1 - you'll see the /noexecute=[policy level] in the boot.ini

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Utilising more than 4GB of RAM with Windows Server 2003 Standard Edition – Enabling /PAE /3GB by DefinIT, unless otherwise expressly stated, is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.

Posted by Sam McGeown