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Virtual Address Space

Virtual Address Space

By default, 64-bit Microsoft Windows-based applications have a user-mode address space of 8 terabytes (7 terabytes on Itanium-based systems). However, applications can specify that the system should allocate all memory for the application below 2 gigabytes. This feature is beneficial for 64-bit applications if the following conditions are true:

  • A 2 GB address space is sufficient.
  • The code has many pointer truncation warnings.
  • Pointers and integers are freely mixed.
  • The code has polymorphism using 32-bit data types.

All pointers are still 64-bit pointers, but the system ensures that every memory allocation occurs below the 2 GB limit, so that if the application truncates a pointer, no significant data is lost. Pointers can be truncated to 32-bit values, then extended to 64-bit values by either sign extension or zero extension.

To specify this memory limitation, use the /LARGEADDRESSAWARE:NO linker option. However, be aware that problems can occur when using this option. If you build a DLL that uses this option and the DLL is called by an application that does not use this option, the DLL could truncate a 64-bit pointer whose upper 32 bits are significant. This can cause application failure without any warning.



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