Enable support for 4GB of RAM (or more) in Vista 32-bit

[francisabey]

On a computer that has 4 GB of RAM, the System Properties dialog box and the System Information dialog box may report less memory than you expect. This problem occurs because the address space is limited to 4 GB in a 32-bit hardware environment. Memory may be relocated to make room for addresses that the basic input/output system (BIOS) reserves for hardware. However, because of this limitation, Windows Vista cannot access memory that is relocated above the 4 GB boundary.

Solution: Open an elevated Command Prompt, type BCDEdit /set pae ForceEnable and press Enter.

The pae parameter enables Physical Address Extension (PAE). On 32-bit versions of Windows, PAE is disabled by default. PAE is an addressing strategy that uses a page-translation hierarchy to enable systems with 32-bit addressing to address more than 4 GB of physical memory. PAE also supports several advanced system and processor features, such as Data Execution Prevention (DEP; "No execute"), Non-Uniform Memory Architecture (NUMA), and hot-add memory, so it is also used on computers with less than 4 GB of memory. PAE must be supported by the processor.

On a computer that supports hardware-enabled Data Execution Prevention (DEP) , PAE is automatically enabled when DEP is enabled and automatically disabled when you disable DEP. To enable PAE when DEP is disabled, you must enable PAE explicitly: Open an elevated Command Prompt.
Type BCDEdit /set nx AlwaysOff & BCDEdit /set pae ForceEnable and press Enter.