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  1. #1

    Difference between different memory types

    hey guys i m confused totally about the memory management in operating systems.
    the tutorial at under memory management
    under section 3.1 "An Abstract Model of Virtual Memory" says
    'In this paged model, a virtual address is composed of two parts; an offset and a virtual page frame number. If the page size is 4 Kbytes, bits 11:0 of the virtual address contain the offset and bits 12 and above are the virtual page frame number. '

    Can anyone pls explain this...
    and also tell the difference between
    physical memory address, main memory address, logical address, virtual address. i m really quite confused...
    or give a link to the tutorial to clarify my doubt... pls.. i need to know them urgently....

  2. #2
    Linux Guru Rubberman's Avatar
    Join Date
    Apr 2009
    I can be found either 40 miles west of Chicago, in Chicago, or in a galaxy far, far away.
    Not a subject that can be learned in a few days...

    1. Physical memory is the RAM in your system.
    2. Virtual memory can exceed the RAM in the system, up to some maximum allowed by the operating system. 4GB on 32-bit systems, 16 exabytes on 64-bit machines.
    3. In a virtual memory system, each program gets its own block of virtual memory, up to the maximum allowed by the OS. See # 2 above.
    4. Program viirtual memory is mapped to system virtual memory which is mapped to physical memory.
    5. How the memory is mapped depends upon the processor, operating system, and other factors. The article in The Linux Documentation Project that you cited was getting into the physical mechanism that Linux uses.

    So, for better / clearer theoretical discussions of virtual memory and its implementation, you should probably read some text books on modern operating system design. There are a number of them (none cheap) that are available from, et al. I would cite some, but I am traveling and my library (I have several good volumes) is at home, 2000 miles from here... Just remember, Google is your friend! Also, you can search on
    Sometimes, real fast is almost as good as real time.
    Just remember, Semper Gumbi - always be flexible!

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