Why to use /3GB Switch in Windows Oracle
Windows 32-bit servers have a problem due to the 32 bit limitation of 2 to the 32nd power (2**32 ~= 2 gigabytes), where Oracle cannot use "above the line" RAM resources.
The 3GB switch only give you an additional two gig, while AWE can go higher
How to Set the /3GB Startup Switch in Windows
Windows Server 2003 includes support for a startup switch that lets you tune the allocation of use of memory and memory address space. Regardless of the amount of physical memory in your system, Windows uses a virtual address space of 4 GB, with 2 GB allocated to user-mode processes (for example, applications) and 2 GB allocated to kernel-mode processes (for example, the operating system and kernel-mode drivers). On systems that have 1 GB or more of physical memory, these two startup switches can be used to allocate more memory to applications (3 GB) and less memory to the operating system (1 GB). This additional virtual address space helps reduce the amount of memory fragmentation in the virtual address space of the Exchange information store process.
To Set the /3GB Startup Switch in Windows Server 2003
1. Right-click My Computer and select Properties. The System Properties dialog box will appear.
2. Click the Advanced tab.
3. In the Startup and Recovery area, click Settings. The Startup and Recovery dialog box will appear.
4. In the System startup area, click Edit. This will open the Windows boot.ini file in Notepad.
5. In the [Operating Systems] section, add the following switches to the end of the startup line that includes the /fastdetect switch: /3GB
6. Save the changes and close Notepad.
7. Click OK two times to close the open dialog boxes, and then restart the computer for the change to take effect.