I've noticed this has been asked many, many times in the past, but I think my question/problem might be slightly different.

Over the last year I've found my Mac has slowed down to a point where it's virtually unusable to all but the simplest of tasks!

So, I did a fresh OS install on a new drive, which I'm running on now. Still the same problem!

On further investigation, I noticed this slowness is down to a memory problem (too much being allocated to the hard disk), and therefore the HD is working overtime to make up for a memory error.

My question is this; I have 5GB of memory under About This Mac/Memory, but only 1GB when profiling within Activity Monitor. Surely, this isn't correct? I know there is small discrepancies, but not this much. Surely there must be a memory error here, as in the computer is not using it's full quota of available memory. Instead, it's only using 1GB.

Please see the attached image, and notice the memory types and slot's I am using - compare memories

Is there anything someone can help or spot here on the memory setup, or errors that would cause this either with hardware or software?

1 Answer 1


I would remove the two smaller DIMMs and see if the Activity Monitor sees 4GB, as it looks as if the 2 2GB DIMMs are not being seen. If this is the case, then keep the 512MBs out and upgrade the RAM, which is very inexpensive these days.

If you're planning to keep this Mac Pro for a while, its worth loading up on RAM even if you don't think you need it, because future OS version may require it. I've always tried to match RAM sizes in all slots, and not mix sizes, and even further, matching the DIMM manufacturer. This may just be an unneeded caution, but you should find out the exact RAM requirements for this particular Mac Pro on the Apple support site.

  • Thank-you! Sorry for my slow response. I have just reseated all my MacPro memory, and et-voila! The system now recognises all 5gb in Activity Monitor. Thank's again for your response, it was most prompting to further investigate faulty memory. Initially, before I reseated the memory, one of the DIMM slots was showing a red light on the circuit board, indicating something faulty.
    – user55014
    Aug 23, 2013 at 12:02
  • Please mark this as an answer to your question. Thanks!
    – IconDaemon
    Aug 23, 2013 at 20:42

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