Physical Address Extension
Physical Address Extension (PAE, Eng. Physical expansion for ( the ) Addressing ) is a technical extension of the field of computer architecture. With PAE you can address more physical memory than the 4 GiB, which can be reached via a 32 -bit address registers in the x86-compatible CPUs 32- bit mode. The usable in a process memory stays with linear memory model ( " flat memory " ) but limited to 4 GiB. The method is used in processors from Intel Pentium Pro and AMD Athlon. Specific enhancements in the paging unit of the CPU to ensure that greater physical addresses are generated.
Support the hardware
Support for Operating Systems
For a meaningful use PAE must be supported by the operating system. However, PAE requires more effort ( time) for the virtual memory management, paging and for 32- bit PCI accesses, the you could save with a limit of 4 GiB main memory. On most computers, but PAE is enabled, despite the limits for memory, because you can use the existing on many processors no- execute bit with PAE. It prevents data from being executed as a program.
BSD family
PAE support in FreeBSD 4.x series starting in 4.9, in the 5.x series from 5.1 and in all 6.x versions and all later versions. The PAE configuration option is needed in the kernel. Loadable kernel modules can be loaded only in a kernel with PAE enabled, if the modules have been created with PAE enabled. Not all drivers support more than 4 GiB of RAM in a system with PAE enabled, run such driver is not correct. NetBSD and OpenBSD (previously only in-current ) PAE support also. All address the full 64- GiB address space.
Haiku
Haiku PAE support since version Haiku R1 Alpha 3
Linux
The Linux kernel includes full PAE support starting with version 2.3.23. Since 2009, PAE is included in many Linux distributions by default, because PAE is required for NX bit.
Mac OS X
Mac OS X for Intel Macs support PAE and the NX bit on all CPUs supported by Apple (from 10.4.4 ). Mac Pro will be delivered up to date with up to 64 GiB of RAM.
Microsoft Windows
PAE is supported on Microsoft Windows 2000 or later (Professional and higher) and XP ( all versions) and this must usually through a boot option enabled. However, while the maximum usable memory is limited to 4 GB on 32-bit versions with PAE enabled. This is the one explained by the fact that it was probably part of the marketing policy of Microsoft. Microsoft, however, justified this restriction so that some of the device drivers used would prepare when accessing memory regions beyond the 4 GB problems.
For the Address Windowing Extension must, depending on the version of Windows may require additional service packs are shown that there are also some unofficial patches for 32-bit Vista and Windows 7, which allow up to 64 GB.
Solaris
Solaris supports PAE from version 7