SQL Server uses the Address Windowing Extensions (AWE) API to support very large physical memory sizes. SQL Server supports up to a maximum of 64 GB of physical memory on 32-bit Microsoft Windows operating systems: Microsoft Windows XP Professional; Windows 2000 Standard Edition; Windows 2000 Advanced Server; Windows 2000 Datacenter Server; Windows Server 2003, Enterprise Edition; or Windows Server 2003, Datacenter Edition.
SQL Server dynamically allocates AWE mapped memory when running with any of the Windows Server 2003 operating-system editions. In other words, the buffer pool can dynamically manage AWE mapped memory to balance SQL Server memory use with the overall system requirements.
AWE addresses a limitation inherent in 32-bit applications: they cannot access more than 4 gigabytes (GB) of process address space. (A 32-bit pointer cannot hold a memory address larger than 4 GB.)
Using AWE, applications can directly reserve physical memory up to the maximum amount allowed by the operating system as non-paged memory. Using AWE allows SQL Server to cache more information instead of reading it from system paging files on disk. This, in turn, provides for performance gains through faster data access and reduces the frequency of disk access.
64-bit applications do not require AWE because access to memory is not limited to 4 GB.
For more information about the AWE API, go to the MSDN Web site, and search on the term "Address Windowing Extensions."
For information about how SQL Server works with non-uniform memory access (NUMA), see Understanding Non-uniform Memory Access.