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Activity Monitor not showing all RAM

I just upgraded to 10.6.3 and then 10.6.8 on my Mac Mini. With 10.6.3 Activity Monitor started showing total of 3 GB of RAM instead of 4 GB as System Profile does show. I ran Rember and all tests passed. It showed 4 GB total memory and 1690 MB available memory which seems consistent with AM's Free memory.

Any ideas why the system seems to "see" (System Profiler) all the memory but not be using it (AM)?


User uploaded file

Stephen

Mac mini, Mac OS X (10.6.8), 1.83Ghz, 4 GB RAM

Posted on Sep 13, 2012 7:02 PM

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22 replies

Sep 14, 2012 8:01 AM in response to Stephen Johnson

Chances are your Mac mini can ONLY use 3 of the 4GB you have installed. My 1.83GHz Core 2 Duo Mac mini has two 2GB DIMMs installed, HOWEVER, I can ONLY use 3GB of that RAM.


My guess is System Profiler is telling you the physical RAM installed, but Activity Monitor is telling you want the operating system is able to see.


This is ONLY a guess, as maybe your Mac mini is different from mine.

Sep 14, 2012 8:27 AM in response to BobHarris

I have a related question about the pie chart.


Here's mine:


User uploaded file


I have 12GB installed. Free at 9.72 + Used at 2.28 adds up to 12GB.


But adding up Wired at 957.4MB, Active at 754.1MB, and Inactive at 632.4MB comes to 2.3GB (rounded). Adding that to the pie chart figure of 11.75 gives a total of 14.05GB, which isn't possible. What does the pie chart figure at 11.75GB represent? It can't be the 12GB minus the Wired, Active and Inactive either, since that would be much less than 11.75. And if it's supposed to be the total of installed Memory, why the missing .25GB?

Sep 15, 2012 10:28 AM in response to BobHarris

BobHarris wrote:


Chances are your Mac mini can ONLY use 3 of the 4GB you have installed. My 1.83GHz Core 2 Duo Mac mini has two 2GB DIMMs installed, HOWEVER, I can ONLY use 3GB of that RAM.


My guess is System Profiler is telling you the physical RAM installed, but Activity Monitor is telling you want the operating system is able to see.


This is ONLY a guess, as maybe your Mac mini is different from mine.


But when I boot back into 10.5.8, all 4GB are there:


User uploaded file


Something changed in 10.6. Maybe I need to do a fresh install or go on and upgrade to 10.7.

Sep 15, 2012 2:10 PM in response to WZZZ

WZZZ wrote:

I have a related question about the pie chart.


I have 12GB installed. Free at 9.72 + Used at 2.28 adds up to 12GB.


But adding up Wired at 957.4MB, Active at 754.1MB, and Inactive at 632.4MB comes to 2.3GB (rounded). Adding that to the pie chart figure of 11.75 gives a total of 14.05GB, which isn't possible. What does the pie chart figure at 11.75GB represent? It can't be the 12GB minus the Wired, Active and Inactive either, since that would be much less than 11.75. And if it's supposed to be the total of installed Memory, why the missing .25GB?

Wired+Active+Inactive = Used. Thus, 9.72+2.28 ≃ 9.7.2+2.3 ≃ 12. The 11.75 is a mucked up AM reading. Check the memory via About this Mac->More info. Mine shows exactly 12 GB.


User uploaded file

Sep 15, 2012 3:08 PM in response to baltwo

System Profiler sees all 12GB. I was concerned I might be in the same boat as the OP, losing some off the top. Either that or AM is messed up. It's always showing 11.75, even on a restart. But, interestingly, Free and Used always adds up to 12.


I can see what the breakdown is later using top, and if it agrees with AM. I might trust top to be more accurate.

Sep 18, 2012 4:18 PM in response to Stephen Johnson

fresh install of 10.6.3 has the same behavior, upgrade to 10.7.4 still inaccurate; different than WZZZ's case my 1GB is missing in both the pie chart and the Free + Used and does not seem to be available for use by the system, though System Profiler continues to show all 4 GB.

I use Virtual PC and it has a slider bar to set the RAM for the PC. It shows a little more than 3.5 GB available though above 3 GB it is highlighted in yellow, as if caution about trying to use it. So I set it to a little more than 3GB, started V PC and watched its usage climb in Activity Monitor. When it reached about 3GB the whole Mac OSX locked.

Here is a related issue and the poster's solution was to switch the riser cards around:

https://discussions.apple.com/thread/2324128?answerId=11022205022#11022205022&tstart=0#11022205

Maybe I need to swap my memory cards around.

Sep 18, 2012 4:58 PM in response to Stephen Johnson

Well, I finally decided to go on and search for the specs on my Mini, even though all 4 GB work under 10.5.8. Here it is:

http://support.apple.com/kb/SP7


"1GB of 667MHz DDR2 SDRAM (PC2-5300) on two SO-DIMMs; supports up to 2GB"


I bought it in 10/2007. Even for that long ago, it seems like 2GB would have been quite limiting. I upgraded to 4GB soon after I got it. So, I suppose that I get anything above 2GB is a bonus.

Seems strange and sad to me but I suppose it is true.

😟

Still will try swapping the cards around... maybe I can get the newer OS and all 4GB back.

Sep 18, 2012 6:48 PM in response to Stephen Johnson

You have the same Mac mini I have, and it can ONLY use 3GB of RAM. The SouthBridge chip used to interface the CPU with RAM, Video, USB, Firewire, WiFi, etc.... is only a 32bit device. Because of this, 1GB of address space is reserved for addressing the I/O devices, which leaves 3GB for RAM.


So while you can install two 2GB DIMMs, the southbridge chip will only make 3GB of that RAM visible to the CPU.


My Mac mini Activity Monitor shows 4GB, but if you add up "Free", "Wired", "Active" and "Inactive" you are always come up with 3GB of RAM. No matter what version of Mac OS X you are running.

Activity Monitor showing 4GB is misleading. It is true you have two 2GB DIMMs installed, but only 3GB is usable.

Activity Monitor not showing all RAM

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