[rescue] FS: Matched pair of 1G MacBook 667MHz SODIMMS

Steve Sandau ssandau at gwi.net
Fri Jun 29 10:20:44 CDT 2007

>> Okay, reading that page, I seem to see that I can go to up to 4  
>> gigs of
>> RAM in my 2Ghz Core 2 Duo Macbook?  Apple's website says they can  
>> go up
>> to 2 gigs (which is what I've got in it right now).  In any case, for
>> a bit over $230, I could double my RAM and give my brother's CoreDuo a
>> bump.  Nice.
> Well, no, it seems that by putting in a pair of 2GB SO-DIMMs you will  
> get the performance boost of having a matched pair, but still only  
> have 3GB available to the system.

Yeah, if this is like the Dell laptops we recently acquired, you can put 
4G of RAM in them, but only have about 3.25 G accessible to the system. 
(The Dell website was not really clear about this, either.)

My understanding (please correct me if I am wrong) goes something like this:

A 32-bit box supports 4G of RAM because that is how much 32 bits can 
address. PCI express needs a bunch of memory addresses to use to map its 
stuff, so it takes the top half gig of *addresses* (not actual memory) 
for its own purposes, thus making the actual memory in that range 
inaccessible. In our case, another quarter gig was used by PCI express 
to map the video card memory, so we were down to 3.25 gigs available.

Dell also told us we should have matched memory DIMMs, so we ended up 
buying 2x2G instead of 1x2G and 1x1G.

The whole thing was very frustrating, especially when we found out 
"that's just the way it is."


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