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MacBook Core 2 Duo and 4.0 GB RAM? What is the real limit?
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Dedicated MacNNer
Join Date: Aug 2001
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I know the November "Late 2007" MacBooks can address 4.0 gb of RAM, but I'm a bit confused by what I see on my Core 2 Duo MacBook (RM7131xxxxxx). I installed a pair of 2.0 gb techworks SODIMMS and now both System Info and Activity Monitor indicate 4.0 of RAM instead of the expected 3.0.
Oh... maybe this is is a Leopard effect! So, I booted into Tiger and it also reports 4.0 gb of RAM.
Was the 3.0 GB limit only for the pre Core 2 Duo machines or is the system merely reporting more RAM than it can actually address?
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Posting Junkie
Join Date: Nov 2000
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Originally Posted by Guy Kuo 
Was the 3.0 GB limit only for the pre Core 2 Duo machines or is the system merely reporting more RAM than it can actually address?
The only MB that can address 4 GB is the latest one. Your previous generation C2D MB is showing 4 GB because that is what is installed. However, if you actually go and launch apps and observe the RAM being gobbled up, you will notice your MB can only address 3 GB.
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Dedicated MacNNer
Join Date: Aug 2001
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It is a bit unnerving to see the system report more RAM than you know it can actually address. If it reported 3 gb, I'd be more reassured that the system wasn't going to try overwriting memory blocks when the threshold was crossed.
Okay.... it seems to work. I just fired up four instances of my own CT reconstruction program, each instance of which use just over 800 MB of RAM. Add to that, Photoshop and a couple other applications and Activity Monitory shows
Free: 15.96 MB
Wired: 388.23 MB
Active: 17.3 MB
Inactive: 889.40 MB
Used: 2.98 GB
Go ahead in put those pairs of 2 gigs in. It does speed up memory intensive situations and the system actually knows to limit itself to 3 gb even if it reports that 4 GB are installed.
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Last edited by Guy Kuo; Nov 11, 2007 at 06:22 AM.
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Addicted to MacNN
Join Date: Feb 2003
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Like you said, the late 2007 MacBooks will use all 4gb of memory.
Does anyone know what the cause of the previous model only being able to address 3gb is? A friend asked and I was unable to answer.
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Posting Junkie
Join Date: Oct 2005
Location: Houston, TX
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The Activity Monitor erroneously reports 4GB under the pie chart; if you look at the pie chart, it's only representing 3GB (note a 1GB catagory will take up about a third of the chart rather than a fourth).
The 4GB limitation is an addressing limitation of the chipset; the chipset only supports 32-bit addressing, but the upper few bits have historically been used for PCI addressing space (and a few other things) leaving you with only ~3.1GB to use (which Apple trims to an even 3GB).
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