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In computing, Physical Address Extension (PAE), sometimes referred to as Page Address Extension, [1] is a memory management feature for the x86 architecture. PAE was first introduced by Intel in the Pentium Pro, and later by AMD in the Athlon processor. [2]
When operating in legacy mode the AMD64 architecture supports Physical Address Extension (PAE) mode, as do most current x86 processors, but AMD64 extends PAE from 36 bits to an architectural limit of 52 bits of physical address. Any implementation, therefore, allows the same physical address limit as under long mode. [11]: 24
Physical Address Extension, an x86 computer processor feature for accessing more than 4 gigabytes of RAM; Power added efficiency, a percentage that rates the efficiency of a power amplifier; Post Antibiotic Effect, the period of time following removal of an antibiotic drug during which there is no growth of the target organism
This allows a large page to be located in 36-bit address space. If Physical Address Extension (PAE) is used, the size of large pages is reduced from 4 MiB down to 2 MiB, and PSE is always enabled, regardless of the PSE bit in CR4.
Many 32-bit computers have 32 physical address bits and are thus limited to 4 GiB (2 32 words) of memory. [3] [4] x86 processors prior to the Pentium Pro have 32 or fewer physical address bits; however, most x86 processors since the Pentium Pro, which was first sold in 1995, have the Physical Address Extension (PAE) mechanism, [5]: 445 which allows addressing up to 64 GiB (2 36 words) of memory.
A workaround first developed in the Pentium Pro, known as Physical Address Extension (PAE), allows certain 32-bit operating systems to access up to 36-bit memory addresses, even though individual programs are still limited to operating within 32 bits of address space. Provided there is enough memory installed, each program can have its own four ...
If PAE is enabled or the processor is in x86-64 long mode this bit is ignored. [14] 5: PAE: Physical Address Extension: If set, changes page table layout to translate 32-bit virtual addresses into extended 36-bit physical addresses. 6: MCE: Machine Check Exception: If set, enables machine check interrupts to occur. 7: PGE: Page Global Enabled
For example, x86 computers can address more than 4 gigabytes of memory with the Physical Address Extension (PAE) feature in an x86 processor. Still, an ordinary 32-bit PCI device simply cannot address the memory above the 4 GiB boundary, and thus it cannot directly access it.