Thread: Virtual Machine

  1. #1
    Pursuing knowledge confuted's Avatar
    Join Date
    Jun 2002

    Virtual Machine

    I'm sitting here reading Teach Yourself Windows 95 Programming in 21 Days, a horribly outdated book, but the best my library has to offer. Anyway, the following paragraph made me curious....

    when you are using a true 32-bit program under Windows 95 or Windows NT, it will run automatically in its own address space. Specifically, each Windows 95 program runs in Virtual Machine that is 4GB. Each program has its own 4GB address space that is not shared by other programs on the system. This provides for a very robust architecture.
    Does anyone know how the virtual machine works? I assume that it is still implemented in current versions of Windows.

  2. #2
    Registered User Codeplug's Avatar
    Join Date
    Mar 2003
    Poor use of terminology. What it is saying is that the process is running in its own virtual address space.

    This article talks about virtual memory under Windows NT.


  3. #3
    Registered User
    Join Date
    Dec 2002
    Consider the programs virtual address space as that programs own sand box. The computer maps all virtual addresses to real memory addresses (or virtual memory - ie swap file). This way, if a program accesses memory location 0x00, and another 32 -bit program accesses 0x00, they are actually 2 different REAL memory addresses.

    This way, if a program perfroms illegal operations and crashes, it only affects it's own sand box.

    16 -bit apps however, all share one sand box in 32-bit windows. Therefore, if a 16 bit app crashes, it can take down other 16 bit apps running on that machine.

    I hope this clears things up a bit.


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