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Thread: 64-bit Ubuntu doesn't recognize all RAM

  1. #1
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    64-bit Ubuntu doesn't recognize all RAM

    I have been using karmic since november and i just noticed >.<.
    Ubuntu only recognizes 3.2GB of RAM.

    All i have found regarding this issue is regarding 32-bit Ubuntu which i already know won't recognize RAM above ~3GB, but i have been using 64-bit OS'es for a long time now because i usually have 4GB of RAM.

    BIOS sees 4GB of RAM without problems.

    Am i missing something?
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  2. #2
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    Re: 64-bit Ubuntu doesn't recognize all RAM

    Have you got a video card that uses shared RAM? From what I have read, that is the most likely explanation.
    Michael

  3. #3
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    Re: 64-bit Ubuntu doesn't recognize all RAM

    I am on a desktop, which has a Geforce 9600 with its own RAM.
    I am not sure but I thought shared memory only applied to laptops, or am i wrong?

    edit:
    uname -a gives:
    Linux alex-ubuntux64-1 2.6.31-20-generic #58-Ubuntu SMP Fri Mar 12 04:38:19 UTC 2010 x86_64 GNU/Linux

    and uname -m gives:
    x86_64
    Last edited by Danimoth; April 12th, 2010 at 12:07 AM.

  4. #4
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    Re: 64-bit Ubuntu doesn't recognize all RAM

    Ok, probably not the video card then (yes, I think there are cards for desktops with shared RAM).

    I have seen a few threads regarding similar questions, but can't remember right now what the reasons for it were. Hang in there, I don't think anything is broken.
    Hopefully someone will turn up who knows a bit more about the subject.
    Michael

  5. #5
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    Re: 64-bit Ubuntu doesn't recognize all RAM

    Ok, thx for your help .

  6. #6
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    Re: 64-bit Ubuntu doesn't recognize all RAM

    Quote Originally Posted by Danimoth View Post
    Ubuntu only recognizes 3.2GB of RAM.
    Ubuntu recognizes whatever the BIOS says is left after the hardware takes it´s share of RAM.
    Video, audio, USB, FSB, BSB, etc...
    then the software stuff...
    pointers, caches, registers, etc
    PAE, etc
    all take RAM.

    Thus and So...
    Whatever is left after the hardware PROPERLY initializes is what the OS will get to use/see.

    (for clarity, I added the following, so future readers may better understand...)

    THEN, whatever is left after the software PROPERLY initializes is what the OS will report as "FREE"

    regarding 32-bit Ubuntu which i already know won't recognize RAM above ~3GB,
    That statement is true only if the kernel AND the hardware do not utilize PAE,
    otherwise, YES 32bit Linux CAN see/utilize more than 4GB of RAM

    Any statement to the contrary is FUD...
    And YES, I am using a 32Bit Ubuntu Hardy with 8GB RAM...
    all 8GB seen and used.


    but i have been using 64-bit OS'es for a long time now because i usually have 4GB of RAM.
    Great, but don´t blame 32Bit Linux, it´s been happily seeing more thatn 4GB for quite a spell...

    BIOS sees 4GB of RAM without problems.
    Am i missing something?
    BIOS uses code to query RAM in order to ´see´ how much RAM exists. Then it starts handing out RAM to various...
    see first part of this post.
    Last edited by egalvan; April 15th, 2010 at 02:32 AM. Reason: clarified: software initialization also uses RAM
    "Free software is a matter of liberty, not price." -- Richard Stallman
    So don't forget to tip your software authors!

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  7. #7
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    Re: 64-bit Ubuntu doesn't recognize all RAM

    Quote Originally Posted by egalvan View Post
    Ubuntu rcognizes whatever the BIOS says is left after the hardware takes it´s share of RAM.
    Video, audio, USB, FSB, BSB, etc...
    then the sofware stuff...
    pointers, caches, registers, etc
    PAE, etc
    all take RAM.

    Whatever is left after the hardware PROPERLY initializes is what the OS will get to use/see.
    Aha, then its not some kind of bug. I was used to seeing 4GB in Windows and didn't know this.

    That statement is true only if the kernel AND the hardware do not utilize PAE,
    otherwise, YES 32bit Linux CAN see/utilize more than 4GB of RAM
    I also knew about PAE from the various threads i encountered just before posting this(before that i didn't know TBH), but i wanted to stress out that the OS was supposed to be able to see all RAM but it didn't, so the "problem" was somewhere else.

    Thank you for the thorough answer .

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