Virtual Address Space

By default, 64-bit Microsoft Windows-based applications have a user-mode address space of several terabytes. For precise values, see Memory Limits for Windows and Windows Server Releases. 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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