Windows® via C/C++, Fifth Edition

Committing Storage in a Reserved Region

After you have reserved a region, you need to commit physical storage to the region before you can access the memory addresses contained within it. The system allocates physical storage committed to a region from the system’s paging file. Physical storage is always committed on page boundaries and in page-size chunks.

To commit physical storage, you must call VirtualAlloc again. This time, however, you’ll pass the MEM_COMMIT identifier instead of the MEM_RESERVE identifier for the fdwAllocationType parameter. You usually pass the same page protection attribute (most often PAGE_READWRITE) that was used when VirtualAlloc was called to reserve the region, although you can specify a different protection attribute. ...