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Meaning of Task Manager "Physical Memory" data

    Question

  • We have a Hyper-V Guest with 16GB of RAM running Sql server.  In Task Manager, Performance pane, I see:

    >>>>>>>>>>>>>>

    Physical Memoery (MB)

    Total          16383

    Cached        4012

    Available     4656

    Free             655

    >>>>>>>>>>>>>>>

    Available = 4656, Free = 655?  Are we running "low" on memory? From an Administrative perspective what is the right value to focus on?

    TIA,

    Barkingdog

         

    Wednesday, May 9, 2012 4:46 PM

Answers

  • Hello,


    The right value to focus on is “Available”.


    Free – This part of memory has nothing at all in it. It’s not being used and it contains nothing.


    Available – This numbers includes all physical memory which is immediately available for use by applications. It wholly includes the Free number, but also includes most of the Cached number. Specifically, it includes pages on what is called the “standby list.” These are pages holding cached data which can be discarded, allowing the page to be zeroed and given to an application to use.


    Cached – Here things get a little more confusing. This number does not include the Free portion of memory. And yet imight see that it is larger than the Available area of memory. That’s because Cached includes cache pages on both the “standby list” and what is called the “modified list.” Cache pages on the modified list have been altered in memory. No process has specifically asked for this data to be in memory, it is merely there as a consequence of caching. Therefore it can be written to disk at any time (not to the page file, but to its original file location) and reused. However, since this involves I/O, it is not considered to be “Available” memory.


    Total – This is the total amount of physical memory available to Windows.


    Thanks
    Zhang

    • Marked as answer by edm2 Thursday, May 10, 2012 4:32 AM
    Thursday, May 10, 2012 3:22 AM
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