MacBook Late 2008 Memory Update

These machines support up to 8GB of memory, but are very picky in that they need PC-8500 (1033 MHz) dRAM, but many folks don’t. First you have to check your model numbers. BTW, the reason you might want to do this is your MacBook is perfectly good and you care about the environment. And/or, you decided to do the $300 Apple full rebuild of your machine. I realize that it is cheaper to buy a new MacBook, but for those of us who like to keep things going, here are the instructions. First, put in an SSD, this is easy and for $100, you get a machine that is probably twice as fast.
Then upgrade the memory. Making sure you have the right firmware.

First, you want to make sure you have one of the affected models:

MacBook 13.3″ 2.0GHz and 2.4GHz

MacBook Pro 15″ 2.4GHz model w/ExpressCard Slot

MacBook Pro 15″ 2.53GHz model w/ExpressCard Slot

MacBook Pro 15″ 2.66GHz model w/ExpressCard Slot

MacBook Pro 15″ 2.8GHz model w/ExpressCard Slot

MacBook Pro 15″ 2.93GHz model w/ExpressCard Slot

Next, check the Boot ROM Version in your System Profiler.

MacBook Pros with a Model ID of MacBookPro5,1 should have a Boot ROM Version of MBP51.007E.B05.

MacBooks with a Model ID of MacBook5,1 should have a Boot ROM version of MB51.007D.B03

Machines with other Model IDs are not affected and don’t need an update.

**IMPORTANT NOTE: EFI Firmware Update 2.8 was released on February 28, 2012 for the Later 2008 MacBook Pro. If you have installed that update, your Boot ROM version will be MBP51.007E.B06. If you have this update installed, you’re already able to install the 8GB without any problems and don’t need to perform further updates to install more RAM.

“Secret” Firmware lets Late ’08 MacBooks use 8GB. | Other World Computing Blog\

Then you have to make sure that you have the right memory because folks will sell you PC-12800 (800MHz) memory as PC-8500 (533MHz) because the 533 isn’t available. The trick is to either buy old RAM that is slow or just leave a true PC-8500 in one slot and this turns down the speed enough. We have some old MacBook Pros with 2GB true PC-8500, so you mix and match. Buy the 1x4GB PC-12800 and then put in an old 2GB stick and you will get 6GB. We used the same trick for our Mac Mini 2010 that had the same problem. We ended up leaving the 2GB PC8500 memory in it and then using a new 8GB module to get to 10GB. Not as good as 16GB but much cheaper. It also needs to run at 1.5V apparently not 1.35V, but that is speculation.

If you bought your RAM at a place that also sells PC RAM you may have gotten mislabelled RAM. PCs can handle different RAM speeds so they’ll often label higher speed RAM as a lower speed rather than make two different speeds of RAM. But Macs are much more picky. They require a RAM stick to be exactly 667mhz not 675mhz or 800mhz. The way to tell is to put one of your old RAM sticks in and it will force the new RAM to run at the correct speed.
This is from one review of PNY RAM:
“These modules are actually 800Mhz. PNY no longer makes or sells 667Mhz modules. Not all computers that require 667Mhz are compatible with 2 800Mhz modules. They refuse to down clock properly. This is especially true with a number of Core 2 Duo MacBooks. Spoke to PNY support, they flat out told me that yes, they sell 800Mhz modules in 667Mhz packaging. If you RMA a module that is 667Mhz (or supposed to be 667Mhz) they will replace it with an 800Mhz module as they no longer have any 667Mhz SODIMMs, not even for RMA replacement!”
Installing 8GB RAM in late ’08 Unibody…: Apple Support Communities

As another aside, it looks like OWC and Crucial still do sell true PC8500 RAM which is ironically much more expensive than PC3-12800 memory at $85 vs. $60. In the end, we got a set of 4GB and spread it out over two MacBooks to get to 6GB which is fine and a much cheaper upgrade with most of the performance benefit.