To be honest, we weren’t very optimistic on this rumor as, by specification, the Intel processors used in these machines list a maximum of 16GB of total memory…and our initial OWC MaxRAM Memory Certification tests didn’t pass.
We started our testing with the base Core 2 Duo (iMac10,1) model and have indeed confirmed that the Core 2 Duo models max out at 16GB of memory. When more than 16GB of memory is installed in those systems, the machine just would not complete booting. The prospect wasn’t looking too good.
But then we tested the other end of the spectrum with the 2.8 GHz Core i7 (iMac11,1) model and that is when the testing started to tell a completely different story.
Not only would our 32GB PC3-8500 DDR3 1066MHz SO-DIMM Memory Upgrade Kit boot the machine, but our testing uncovered that the machine was able to fully utilize all the RAM without any slowdowns. After testing our way through all the different models and all the different iterations of OS X that are compatible with these iMacs, we concluded:
The quad-core Intel i5 & i7 iMacs were able to address and fully utilize 32GB of OWC memory when running 10.6.3 or later once the latest updates were applied.
There is one caveat for those running 10.6.x – you MUST be running 64-bit mode in order to address all 32GB. In 32-bit mode, all 32GB will show, but only 16GB will be utilized. See our post Just Say “Know” when it comes to Snow Leopard’s 64-bit mode for more details on 32-bit vs. 64-bit mode.
How do you ensure your Late ‘09 iMac can address 32GB of RAM?
Check the Model ID of your iMac. If it is iMac11,1 simply run Software Update to make sure you have the latest version of OS X 10.6, 10.7, or 10.8 with any accompanying firmware updates. We recommend keeping these up to date regardless of whether or not you intend to upgrade to 32GB.
Then, you just need the proper specification of memory modules such as the OWC 32GB PC3-8500 DDR3 1066MHz SO-DIMM Memory Upgrade Kit. It’s that easy.
And, yes, the additional memory is available to Windows via Bootcamp, too.
As always…Happy Upgrading!