Physical Address Extension (PAE) and application memory tuning

Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2

Physical Address Extension (PAE) X86 and application memory tuning

Physical Address Extension (PAE) X86 and application memory tuning, also known as 4-gigabyte tuning (4GT), are complementary technologies for computers that use Intel processors.

Application memory tuning provides more of the computer's virtual memory to applications by providing less virtual memory to the operating system. PAE X86 allows software using the Address Windowing Extensions (AWE) API set running on a computer with an Intel Pentium Pro processor or later and either Windows Server 2003, Enterprise Edition, or Windows Server 2003, Datacenter Edition, to map more physical memory into the application's virtual address space.

For example, if you have a computer with a Pentium Pro processor or later and 16 gigabytes (GB) of physical memory (the maximum amount supported by application memory tuning), you can use application memory tuning to allocate 3 GB of virtual memory to applications (leaving 1 GB for the operating system). A given application can then lock the physical memory. Using the AWE API set and the PAE X86 kernel, the remaining 12 GB of physical memory is available to the application for caching purposes. Consequently, the application can access up to 15 GB of physical memory.

For more information, see:


  • On computers with more than 16 GB of physical memory using application memory tuning, physical memory above the 16 GB address is ignored by the operating system. For more information, see Enable application memory tuning.


  • This topic does not apply to Windows Server 2003, Web Edition.