Memory Management Under WOW64

Memory management under WOW64 depends on the processor architecture.

Itanium Support

WOW64 simulates 4 KB pages on top of the native 8 KB pages that the Itanium processor uses. The processor assists by providing excellent simulation with low overhead. The simulation code cannot handle the following cases:

• Write tracking. The GetWriteWatch and ResetWriteWatch functions are implemented in the kernel using native page-size granularity, which means the WOW64 4 KB page simulation cannot determine which simulated 4 KB pages are written within the underlying 8 KB page.
• Address Windowing Extensions (AWE). The AWE functions operate on page numbers, and there is no way to map 64-bit page numbers to 32-bit page numbers.
• Section alignment. For executable images with section alignment smaller than 8 KB (the default is 4 KB for x86 images), WOW64 must dirty all image pages. This effectively copies each page to the page file, and prevents read-only image pages from being shared between processes.
• The ReadFileScatter and WriteFileGather functions are not supported.

x64 and ARM64 Support

The native page size is 4 KB. Therefore, the following are supported:

• The GetWriteWatch and ResetWriteWatch functions are supported.
• The ReadFileScatter and WriteFileGather functions are supported.
• There are advantages to using large addresses because x64 WOW64 supports a 4 GB virtual address space.

Related topics

Memory Limits for Windows Releases

4GT RAM Tuning