Virtual address space in 64 bit systems running in compatibility mode

Question

I saw that on a 64 bit windows OS the user virtual address space available is 8 terra bytes. But if the program we are executing on this is running in 32 bit compatibility mode is this much of user space still available ? or does it behave like a normal 32 bit OS and gives only 2GB user address space?

Answer 1

Microsoft has a chart showing the various limits: Memory Limits for Windows Releases

To summarize just the user-mode virtual address space:

• 32-bit Windows:
  • 32-bit process: 2 GB by default; 3 GB with /LARGEADDRESSAWARE:YES and 4GT
• 64-bit Windows (x64 architecture):
  • 32-bit process: 2 GB by default; 4 GB with /LARGEADDRESSAWARE:YES
  • 64-bit process: 8 TB by default; 2 GB with /LARGEADDRESSAWARE:NO

4GT is 4-gigabyte tuning:

• XP: /3GB boot.ini switch
• Vista: bcdedit /set increaseuserva 3072

Mark Russinovich made a blog post explaining many these limits: Pushing the Limits of Windows: Virtual Memory