Why does my Mac show 3.75GB of RAM when I have 4GB of memory installed?

Nov 19, 2010 - 6 Comments

3.75gb ram instead of 4 You may have noticed that some Mac models display 3.75GB of RAM in the Activity Monitor when they have 4GB of RAM installed, but why is this? The answer is simple: your Mac has a GPU that uses shared memory. This means that your graphics card borrows some of the systems memory and uses it exclusively for graphics processing, this kind of GPU with memory sharing is common on the iMac, Mac Mini, MacBook, MacBook Air, and the 13″ MacBook Pro model.

In fact, even if you upgrade your RAM you will continue to have the shared memory amount missing from the available RAM within Activity Monitor, as a result if you had an 8GB upgrade it would show 7.75GB of RAM. This is not an indicator of anything being wrong or of having bad RAM, it’s perfectly normal. The only problem with a GPU borrowing RAM is that you may run out of available system memory faster, but you can easily check to see if your Mac needs a RAM upgrade and whether or not you’d benefit from adding additional memory.

I’ve had multiple people ask me this question, so if you were curious too, now you know.

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Posted by: William Pearson in Mac OS X, Troubleshooting

6 Comments

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  1. Zach says:

    I had always assumed this was some discrepency between using 1024^3 bytes per gigabyte vs 1000^3 bytes per gigabyte.

    Comes out close for 4.0 GB

    4.0 * 1000^3 / 1024^3 = 3.73

    But if 8.0GB is showing as 7.75GB then I guess it is the video card because 8.0 * 1000^3 / 1024^3 = 7.45 GB

  2. John says:

    The only problem that i have with this article is that i just checked on my friends macbook pro. Same model and everyting and his activity monitor is showing 4.0gb instead of 3.75gb. Can you explain that?

  3. […] En uso: es la memoria real que tiene el sistema operativo. Yo tengo 4GB, pero marca menos porque lo que falta es la memoria que usa mi tarjeta gráfica, tal y como explican en este post. […]

  4. lui says:

    the missing 250 mb are used by the internal graphics card, it has nothing to do with the 1000 mb per gb, it is always 1024.

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