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 problem arose with Windows 2000 Advanced Server where workloads exceeded the 2TB address capability of the 32-bit address space. The Pentium III Xeon. can support 64GB of memory but that was done by using the extra bits available with the segment registers. Windows Server 2000 advanced server supports 8GB of memory and the data center version supports up to 32GB.
So MSFT added the /LARGEADDRESSAWARE[:NO] option to the computer and linkers for Visual C++.
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)
Intel introduced the iTanium CPU on May 29, 2001 as a new platform for servers. The main objection was the backwards compatibility was hampered by a significant speed penalty with existing software make the CPU a slow seller. Intel supports the iTanium for servers which are often in use for very long periods of time.. Intel finally released the last iTanium in 2017.
AMD instructed their Opteron CPU on April 22, 2003.
- native execution of legacy x86 32-bit applications without speed penalties
- native execution of x86-64 64-bit applications
AMD also introduced RISC class capabilities into the 64-bit capable core. By combining these two capabilities, the Opteron earned recognition for its ability to run the vast installed base of x86 applications economically, while simultaneously offering an upgrade-path to 64-bit computing. Intel eventually licensed the AMD 64-bit solution in a cross licensing deal.
Visual Studio 2003 provided a command line compiler to support AMD64. Visual Studio 2005 fully supports AMD64 projects. Visual Studio 2005 also supports iTanium.