In late 2009, an EFI Firmware Update was released [by Apple] 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.
Whether any other elements were affected by this change is undetermined, but it did change memory addressing; with the later version of the update installed, you could address a full 8GB in Snow Leopard. Unfortunately, Software Update doesn’t show this version as being different from the previous one, so users wouldn’t be notified if they had already updated their firmware to the older version.
The practical upshot of all this is that if you installed the EFI Update when it first came out, like we did, you would have gotten the old code, which meant your computer would only address 6GB properly. Those who didn’t upgrade until after Apple changed the updater got the newer firmware, which allowed proper addressing of 8GB.
Once we manually installed the “updated” version of the EFI Firmware in our test machines, they were able to address 8GB normally, without any crashing or slowdowns.
Read more in the full article, which explains how to ensure your Late ‘08 MacBook/MacBook Pro can address 8GB of RAM, here.
[Attribution: iClarified. Thanks to MacDailyNews Reader “Edward W.” for the heads up.]