Do not play memory games : deploy front end/application servers on 64-bit

I was recently visiting a large customer who had multiple Web Front End/Application servers (combined PWA and PSI) and each server had 12GB of memory. They were using Windows Server 2003 32-bit version.

In a 32-bit environment only a fraction of the RAM was being utilized and it's important to remember that the /3GB is not supported either: The Windows Server 2003 /3GB switch is not supported in Windows SharePoint Services 2.0 or in later versions or in SharePoint Portal Server 2003 SP2 or in later versions

As stated in the SharePoint documentation: if you are running 32-bit front-end Web servers, we recommend that you do not use the /3gb switch in Windows ServerĀ® 2003 to change the 2 GB of virtual address space to 3 GB for all user mode processes. We recommend against using the /3gb switch because most SharePoint site traffic involves sending large amounts of data through the operating system, and leaving only 1 GB of address space for the operating system can destabilize the computer.

So in the end the only option is to re-install the servers on a 64-bit operating system like Windows Server 2008 for instance :)

I encourage you to check the following article on MSDN: Memory Limits for Windows Releases