In a blog post published last week, Other World Computing unravels a mystery that has seen conflicting information over whether "Late 2008" aluminum MacBooks and MacBook Pros support a maximum of 8 GB of RAM. According to the report, Apple apparently quietly changed a December 2009 firmware update for the machines at some point to boost maximum RAM support from 6 GB to 8 GB.
The discovery comes after numerous reports, including some in our own forums, pointed to 8 GB of RAM being supported in these machines even though OWC's earlier testing had clearly shown that a maximum of 6 GB could be addressed even with 8 GB installed.
Not being the type to just let these sorts of claims to go unchallenged, we went back to our testing lab, grabbed the affected model machines, running 10.6.6. and dropped an 8GB upgrade kit in them.
The results were exactly the same as in 2009, lending credence to our conclusions, but the sheer number of claims to the contrary led us to continue searching - and the trail ended at Apple.
In late 2009, an EFI Firmware Update was released to address the buzzing noises coming from the optical drive. However, it seems that somewhere along the line, Apple changed this update without notating it anywhere.
Consequently, OWC recommends that users of Late 2008 MacBooks and MacBook Pros interested in upgrading to 8 GB of RAM check System Profiler on their machine to determine whether they are running the latest Boot ROM versions of MBP51.007E.B05 (MacBook Pro) or MB51.007D.B03 (MacBook), and if not, re-download the EFI firmware update and apply it to their machines.
Affected machines introduced in late 2008 include MacBooks running at 2.0 GHz and 2.4 GHz, as well as 2.4GHz 15" MacBook Pros and 2.53 GHz and 2.8 GHz MacBook Pro models offering ExpressCard slots.