system memory, what's it all about?

Discussion in 'MacBook Pro' started by Becky10, Aug 5, 2013.

  1. Becky10 macrumors newbie

    Joined:
    Aug 4, 2013
    #1
    Hi, Im trying to get to grips with how my macbook works and so on... And I have been looking at the 'system memory" thing, and I was wondering if someone could explain it to me, and in particular what VM size is, and also how page ins and page outs work.
    Thanks
     
  2. wabbit42 macrumors regular

    Joined:
    Jun 25, 2012
    #3
    Page outs occur when the system wants more RAM than you have available. I believe it results in writing the data to the disk temporarily - someone will probably come along to confirm. The fewer page outs you have, the better (preferably zero).

    Free memory and inactive memory is RAM that can be used by the system, wired and active memory is currently being used. The inactive memory is basically when you close a program, it is kept in the RAM so if you open it again it will open more quickly - but this inactive memory can be 'overwritten' by other tasks if needed (like how deleting a file works).
     
  3. jdsipod macrumors member

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    Feb 25, 2011
    Location:
    Iowa City, IA
    #4
    From this month's issue of MacLife, hopefully this helps
     

    Attached Files:

  4. Becky10 thread starter macrumors newbie

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    Aug 4, 2013
    #5
    Ah yes that is exactly what I needed, thanks, a lot clearer now, though I'm still not clear what the VM size is about... anyone know?
     
  5. jdsipod macrumors member

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    Feb 25, 2011
    Location:
    Iowa City, IA
    #6
    VM or Virtual Memory, is used when all of your physical RAM is being used, but the computer needs more, so it starts saving information temporarily to your hard drive. Basically it allows for more RAM to be used then there is actually on your computer.

    Does that make sense?
     
  6. Becky10 thread starter macrumors newbie

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    Aug 4, 2013
    #7

    So does that mean that information, (like applications that are open i mean) are stored on RAM if there is enough space and in the VM and on the hard drive?
    I shut my computer down last night, and now when I look at the "system memory" it says that I have 2.48 GB free, and that my VM size is 152.61 GB...
    Is the VM the potential space I could be using or the space I can actually use?
    sorry, probably stupid questions, I find it all a bit confusing...
     
  7. leman macrumors 604

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    Oct 14, 2008
  8. jdsipod macrumors member

    Joined:
    Feb 25, 2011
    Location:
    Iowa City, IA
    #9
    That actually is a pretty good question. After shutting down your computer, it is normal for the amount of free RAM and the size of VM to change. Basically RAM is where temporary information like user settings and application processes are stored but are not written to the hard drive. This allows for faster access to this information than having to read it off of your hard drive. When you shut your computer down anything that is stored in RAM is erased, that's why it changes.

    Now for VM, lets say you have 4GB of physical RAM, and you start using a bunch of different applications, and you use up all of that. Now your computer starts using your Virtual Memory, which is space that is allocated on your hard drive, that acts just like physical RAM, but only exists temporarily. This allows your computer to exceed the size limit of your physical RAM. Since it is stored on your hard drive, accessing Virtual Memory is slower than accessing your physical RAM.
     
  9. Becky10 thread starter macrumors newbie

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    Aug 4, 2013
    #10

    Ok, thanks, I think I get it! though there is still one thing that I dont understand. Why when I turn my computer on do I already have a lot of VM?
     
  10. jdsipod macrumors member

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    Feb 25, 2011
    Location:
    Iowa City, IA
    #11
    I can't give you a definite answer for that question, I would assume though that your computer is allocating it from startup just in case it needs it at any point in time, so you don't have to wait while your computer has to create the VM before it is able to be used. Although just because you have a large amount of Virtual RAM right away doesn't mean that it is using it right then and there. I have 16GB of RAM in my computer and my VM size is constantly around 250gb, even though I never have to use it.
     
  11. Becky10 thread starter macrumors newbie

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    Aug 4, 2013
    #12
    Ah yeah that would make sense... Thanks!
     

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