Getting 32-bit Windows to recognize anything beyond 2GB of installed RAM is a seemingly futile effort. Even if your hardware supports the possibility, the software may hold you back – and performance gains are questionable:

The reduction in available system memory depends on the devices that are installed in the computer. However, to avoid potential driver compatibility issues, the 32-bit versions of Windows Vista limit the total available memory to 3.12 GB. If a computer has many installed devices, the available memory may be reduced to 3 GB or less. However, the maximum memory available in 32-bit versions of Windows Vista is typically 3.12 GB.

So, people use a PAE switch to get past the imposed 2GB barrier. Here’s a description of the 4 GB RAM Tuning feature and the Physical Address Extension switch:

When the /3GB switch is used with Windows XP Professional, with Windows Server 2003, Datacenter Edition, with Windows Server 2003, Enterprise Edition, the /3GB switch works identically across versions. This functionality lets device-driver developers test their drivers in this configuration without having to install one of the Windows Server 2003 products just listed. The user-mode memory space is now limited to 3 GB.

Sounds good, right? Not so fast:

The /3GB switch can cause some applications to have problems that are related to address dependencies or to a reduction in kernel space.

Bottom line: if you have 4GB of RAM in your system (or more), and you want to take full advantage of it, start using a 64-bit OS.

32-Bit Windows and 4GB of RAM

For months, I’ve had people asking about the 4GB vs 2GB RAM scenario. The answer isn’t all that simple when it comes to 32-bit flavors of Windows, but despite the language barrier, Aqud does his best to explain it to the community again:

Windows addresses a maximum of 3,37GB at my server, this was due to DEP (Data Executing Prevention) who uses up a few of the 4GB addressable addresses. To expand the addresses you can make advantage of PAE (Physical Address Extension). With PEA windows “supports” up to 8GB of RAM. At windows 2k3 server this option goes on by default at inserting for 4GB ram. This allows windows to make use of ALL the 4096MB’s. What doesn’t change is the kernel mode. Windows has a built-in maximum of 2GB for kernel mode. By using the /3GB switch the kernel mode even gets decreased to 1GB. Even with PAE and 8GB of memory the kernel mode doesn’t use more then 2GB (or 1GB with the /3GB switch on). This is why a Windows terminal server has a maximum of a couple of hundred users, even if it could use 32GB of ram, since the kernel mode wont use more then 2GB. Only solution to this problem is using x64. For your problem, just turn on PAE and its solved. You can turn on PAE by using the /PAE switch at boot.ini, you can also turn of DEP to decrease the amount of used memory mappings, but it will still use a few.

4GB RAM in Windows?