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Physical Address Extension (PAE)

Physical Address Extension (PAE) is a processor feature that enables x86 processors to access more than 4 GB of physical memory on capable versions of Windows. Certain 32-bit versions of Windows Server running on x86-based systems can use PAE to access up to 64 GB or 128 GB of physical memory, depending on the physical address size of the processor.

The Intel Itanium and x64 processor architectures can access more than 4 GB of physical memory natively and therefore do not provide the equivalent of PAE. PAE is used only by 32-bit versions of Windows running on x86-based systems.

With PAE, the operating system moves from two-level linear address translation to three-level address translation. Instead of a linear address being split into three separate fields for indexing into memory tables, it is split into four separate fields: a 2-bit bitfield, two 9-bit bitfields, and a 12-bit bitfield that corresponds to the page size implemented by Intel architecture (4 KB). The size of page table entries (PTEs) and page directory entries (PDEs) in PAE mode is increased from 32 to 64 bits. The additional bits allow an operating system PTE or PDE to reference physical memory above 4 GB.

In 32-bit Windows running on x64-based systems, PAE also enables several advanced system and processor features, including hardware-enabled Data Execution Prevention (DEP), non-uniform memory access (NUMA), and the ability to add memory to a system while it is running (hot-add memory).

PAE does not change the amount of virtual address space available to a process. Each process running in 32-bit Windows is still limited to a 4 GB virtual address space.

Check if PAE is supported

To see if your version of Windows supports PAE, check out which kernel file exists in %SystemRoot%System32:

Ntkrnlpa.exe    PAE Supported
Ntoskrnl.exe    PAE Not Supported

System Support for PAE
PAE is supported only on the following 32-bit versions of Windows running on x86-based systems:

  • Windows 7 (32 bit only)
  • Windows Server 2008 (32-bit only)
  • Windows Vista (32-bit only)
  • Windows Server 2003 (32-bit only)
  • Windows XP (32-bit only)

Check if PAE is Enabled

Open regedit.exe and locate registry key value

HKLMSystemCurrentControlSetControlSession ManagerMemory ManagementPhysicalAddressExtension

If this REG_DWORD value is set to 1 then PAE has been enabled.