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Firmware update to fix 3 GB memory barrier

It appears that some iterations of this version supported only 3 GB of RAM (mine), and some later ones supported 4 GB. The very similar A1226 supported up to 6 GB supposedly.

Is there an unpublished firmware update that will get me up to the 4 GB usage at least? Would it be possible to apply a firmware for a very similar but later Mac to this one and have it work (I know this won't work for systems that are different)?


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From what I understand, the chipset supports 6GB. However, it does not mean all models support 6GB. Going to 6GB of RAM will depend on the model and firmware. This model particularly does not support it, so you are limited to 3GB.

If you do not care about stability or having your new memory downclock to the existing modules, you can save some money and reuse part of the old RAM. However, this is not the best idea since the machine probably came with 667MHz memory. You are likely better off buying 2 similar modules that are 2GB and 1GB in size. The new memory will not downclock this way, but if it's off just enough it can be a problem if you need system stability. If you need absolute stability, buy a 4GB matched pair. The big thing is to try and brand match the memory and CAS latencies.

However, even if you could the RAM would be expensive anyway. The cost of DDR2 in sticks larger then 2GB tends to be pretty expensive these days. Even if you could you would need to weigh the cost to get the memory to do it anyway. It will be much more cost effective to stop at 4GB nowadays.

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Correction! This systems limit is 3 GB of addressable RAM.

Yes, you can put into it two 2 GB modules (4 GB) but only 3 GB is usable to the system. Yes, using two matched modules two 2 GB) is a good idea as the system is then able to use interleaving which is a bit faster than trying to use to mis-matched modules.


Corrected, @danj. I do however, kind of disagree on matching modules. Unless there's a substantial price gap by using a kit, it will be more economical to fudge it and mix sticks. DDR2 is getting a little expensive, so this is more viable then it used to be in some cases.

I still wouldn't recommend it in a setting where stability matters because there's always the chance it could be different enough to go wrong but the majority of 2007-2008 MBP non-Unibodys left these environments years ago. The majority of surving machines that are in use are mostly used in a home environment where there's fault tolerance. I also added it's not a good idea to mix and match if you need stability for good measure.


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