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Asked: 2026-05-11T05:01:40+00:00

I saw that on a 64 bit windows OS the user virtual address space

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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?

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  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

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