Late 2009 Core i5 & i7 iMacs OWC MaxRAM Certified To 32GB Of Memory

The OWC Test Lab technicians have been at it again. After hearing a few forum whispers of 32GB of memory working in the Late 2009 iMacs, we started our own investigation into the matter.

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.

OWC MaxRAM Testing in progress under OS X Snow Leopard.

OWC MaxRAM Testing in progress under OS X Lion.

OWC MaxRAM Testing in progress under OS X Mountain Lion.

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!


  • Most online comment or rumors about the so-called “late 2009 iMac” is worthless because there were four different models (core 2 duo 3.06 and 3.33, core i5, core i7). As the above test shows, the core 2 duo version E7600 ( ) cannot run 32GB.

    All of the 27″ late 2009 iMacs except the slowest core 2 duo 3.06 however have a 1333MHz bus. Even the core 2 duo 3.33 E8600 ( ) has a 1333MHz bus. Thus, there should be no problem running a faster memory stick in any EXCEPT the 3.06GHz core 2 duo. Which is the cheapest of the four “iMac late 2009” models and probably the most common.

    Thus for the E7600 only the 1066MHz RAM would be maximum. Other RAM would just be throttled down to 1066MHz. So there is no point using anything faster than DDR3 PC3-8500S which maxes at this speed. (the “3” in “PC3” means DDR3).

    All faster RAM has several “JEDEC” modes you can see, one of which is the “SPD” the actually accesses the RAM at. You can actually hard set this with some devices, and any good computer will throttle down a memory stick to run at the right speed. Apple however seems to take its cue from the memory stick in the first or special slot, and try to run all RAM at that speed. It’s usually best to use all the same speed of RAM although if you want to experiment, by all means try.

    From the simple fact that the bus speed in the core 2 duo 3.06 E7600 is 1066MHz and the L2/L3 cache is half as large (3 not 6MB as on the E8600) I’d expect the 1333MHz memory to run at 1066MHz. But, there is no such thing as “1333MHz memory”. There is, rather, a spec with a name like PC3-8500S, -10600S, -12800S, -13500S that indicates how many JEDEC modes a stick has, and what frequencies it responds at. Timings are other numbers after this stated on the stick.

    When referring to Mac models, use the actual model number. When referring to memory sticks, use the actual spec name, not nonsense phrases like “1333MHz memory”. When diagnosing timing problems, look at the JEDECs using a program like CPU-Z on a PC.

    And while I will probably try to put PC3-12800S memory into an iMac 3.06 core 2 duo E7600, I won’t expect it to run at 1333MHz, because it can’t. Period. That’s why there’s no point buying any faster RAM than PC3-8500S for an E7600.

    If however you have an E8600 (the core 2 duo 3.33GHz) or the core i5 or i7 models, you have a 1333MHz bus and thus should use PC3-10600S RAM at least. If you use something faster, it may work better, but the timings may be off, or there may be no JEDEC to match Apple’s SPD. If you understand that, you will have no further problems. If you don’t, you should ask someone who does to read this, and not try it yourself.

    • I think your comment contributes something positive to this discussion, mentioning the low end DuoCores in the late 2009 iMac lineup. However, whenever I mention my own “late 2009 iMac” I tend to also add that its CPU is an i7. Furthermore, the title of this blog post we all are commenting on is “Late 2009 Core i5 & i7 iMacs,” which makes it abundantly clear that RAM can operate in this particular iMac at 1333MHz. All said, I’ve been running RAM in my late 2009 iMac i7 at 1333MHz for several years. It runs fine. And yes, I edit video and know how to push the machine too. 1333MHz RAM works and doesn’t cause problems on my late 2009 i7 iMac. And I am not alone. It won’t change your iMac into a speed demon, but I’m a believer in “every little bit counts.” So if you are planning to upgrade RAM in this particular iMac, why NOT put 1333MHz RAM in it! I did, and I have no regrets.

  • Why do you only recommend DDR3 1066MHz RAMs in iMac late 2009 with Core i5 750? Will 1333MHz not work?

    • In the late 2009 iMac (11,1) model, we only recommend using 1066MHz RAM.

      • I understand OWC wants to avoid product returns and avoid being accused of spreading misinformation, but you’re playing it too safe and too by-the-book. Read my previous replies here. 1333MHz RAM works in that particular iMac, and I know this from years of first hand experience. There are no overheating or crashing issues at all. 1333MHz RAM works as perfectly in that late 2009 iMac as the recommended slow-poke 1066MHz RAM.

  • My Mac shows a slightly different spec. It is: 2.66 GHz Core i5 (iMac11,1). I am asking this question simply because it seems to be a model that’s “between” the two abovementioned models that were tested.

    Will the 32GB upgrade work for me since my Mac *model* is the 11,1?

    Or is the intel core i5 the issue?

  • Will DDR3 1333MHz RAMs work in iMac late 2009 with Core i5 750?

  • Will Late 2009 27″ (11,1) will work with Yosemite & 32G of Ram?

  • I’m thinking of upgrading the ram (2x4gb) in my late 2009 iMac i7 (iMac11,1) to 32gb, can I use the existing 2x4gb to upgrade my mid 2010 macbook pro (MBP 7,1) from 4gb to 8gb?


    • The MacBookPro7,1 and iMac11,1 use the same 1066Mhz DDR3 memory, so you may use the memory from the iMac in your MacBook Pro.

      • Updated my late 2009 27 inch iMac i7 quad core from 8 GB to OWC 4 X 8 GB (32 GB total) memory modules about a month ago. Followed video instructions and machine booted flawlessly showing 32 GB RAM the first time and every time since. I can now run OS X Mavericks 10.9.2, Windows 7 (VMWare Fusion 6.0) and TeamViewer with my work desktop loaded and carbonate in the background simultaneously with more than 10 GB free memory unused and many, many fewer SPOD waits. I highly recommend the OWC 32 GB upgrade to the iMac 11,1 series. The OWC web site has all the information necessary to do the job right the first time and their research and experience are not overstated in any way.

  • Will a higher PC3 12800 work for 09 2.8mhz quadcore 2374?

    • We only recommend 1066mhz modules for the late 09 iMacs. 1600mhz modules theoretically should down clock to the iMac’s 1066mhz speed though.

    • I ultimately purchased 1333MHz RAM for my late 2009 iMac 2.8GHz i7 Quadcore, despite the fact Apple does not claim to support it and despite OWC’s cautionary words. For the past 10 months it has been working fine, with no crashes or overheating issues at all. I ran benchmarks before and after which show greater performance after my upgrade to 1333 RAM, which seems to prove the 1333 RAM is indeed being clocked at 1333 and not being down clocked to 1067. I posted further details on Apple’s forum here:

  • I have a late 2009 27″ iMac 11,1 2.8 GHz Core i7, upgraded with OS X 10.9.2 Mavericks. I assume this machine will also run 32 GB upgrade kit specified above, though the article was written prior to Mavericks’ release. It is, of course, later than 10.6.3.

    Not familiar with EFI, but I assume from the article that this is upgraded automatically when the OS is upgraded/updated.

  • Hi,

    I have an iMac 27 11,1.
    I am running latest update of Lion 10.7.8, and there is no EFI update avail.
    So I understand I should be all set correct ?

    Also, the reason why I am looking for an upgrade is that after years of running fine, the machine started to reboot spontaneously. I understand these are often RAM issues. Is that your opinion ?

    I have installed 16GB of 3rd party RAM 3 years ago.
    So may be it is starting to go … ?

    Thank you for any feedback. I understand you can’t say for sure that this is the problem, but any “opinion” would be appreciated.

    Thank you!

    • 8Gb sticks will work in an iMac 11,1 with an iCore 5 or iCore 7 processor. 8GB sticks will not in an iMac that is running iCore 3.

      Defective RAM can be one of many components that can cause a machine to spontaneously reboot. I would recommend running a 3 loop test on your RAM with Rember.

      If you would like additional support, we encourage you to contact our technical support department via live chat, or email, or by telephone at 1-800-275-4576 | 1-815-338-8685

  • Hello, I work on a 2.8 GHz Core i7 iMac (iMac11, 1) 8Gb RAM, Snow Leopard with 64bit architecture on, and I would like to upgrade to 32gb of RAM.
    I have read that to do this I need to have the latest EFI installed and do not know what is this version I need and where to find it. I tried downloading the update iMac (27-inch) – EFI Firmware Update 1.0 but can not find it in the apple help page.
    Then I need to know, what is the version of EFi I need to have installed to upgrade my iMac to 32Gb of RAM?
    And, I can buy 32.0GB (4 x 8.0GB Kit) PC3-8500 DDR3 kit for Late 2009 iMac11, 1 models from europe?
    Thanks, excellent help and website.

    • Good questions here. You can check the latest firmware for your iMac here – That link also has the links to download the latest firmware. Firmware updates should be automatically downloading through your software updates as well.

      The European iMac11,1 should have no issues with the 32gb of memory if the appropriate OS and firmware are on it.

  • I have an 11,1 iMac with Intel Core i-5 processor currently running 16GB RAM, and Mountain Lion 10.8.4
    According to this post, I should be able to upgrade to 32GB RAM.
    If I upgrade to 32GB RAM, will this be available to Parallels?
    Under Parallels I am running Windows System 7 in 32 bit mode.

  • I just upgraded the ram from your 16gb kit and it works like a charm! Yay! I have the late 2009 iMac i7 model and now it is showing:

    Memory 20GB 1067 MHz DDR3.

    I’ll upgrade to 32gb when the budget permits but right now, it is soo fast!

    Sweeeet!! Thanks OWC. :)

  • Will the 8500 1333DDR3 chips work in the 11,1 i7 iMac instead of the 1067mhz? Would there be any advantage to this at all?


  • How about iMac Core i3 Mid 2012?
    Core i5 and Core i7 models only?

    • This article is regarding the 2009 iMac models with model ID: iMac11,1 – not the latest 2012 models.

      That said, the iMac line didn’t include an Intel Core i3 option since 2011. So, which model were you meaning to refer to?

  • Can I just add the 8GB RAM in pairs? I currently have 4+4+2+2=12GB in my late 2009 i7 iMac. Can I replace my 2GB RAM so I have 4+4+8+8=24GB? Thanks.

  • Any thing on the 2010, 11,3?

    That would be super