Chosen Solution
I had a dying Seagate hdd starting to fail, I replaced the hdd with a ssd. I preloaded the ssd with High Sierra. I booted up the iMac with the ssd as the boot drive, no problem. hdd removal, and ssd install went great, on restart I am now missing half (two 4gb ram sticks memory) of my 16gb. Two of the slots show “Empty” Regardless of which slots I put the memory in (ie, i remove two sticks from the left slots and start up, the right two slots show 4gb each. Moe those sticks t the left slots, restart, the right two show empty. Now I place the first two sticks in the left slots with the sticks i removed, restart, they show up a two 4gb memory. Move them to the right two slots, they show as two 4gb memory. No place the two sticks back in the left slots, and they show empty. Remove the right two sticks the left now show up. Any configuration of more than two 4gb sticks shows only two “full” slots and two empy. So the ram sticks are “good” The slots are “good”. I re-initialized the ssd and installed El Capitan (what the iMac was running on prior to switching the drives.). No change. I did the PRAM/NVRAm and SMC resets, again no change. I ordered two new sticks of ram, just to test the possibility of bad ram? And on some forums it was suggested the HS update updated the firmware to “weed” out sub-performing accessories like ram, HD’s, etc. Is it possible to downgrade to perhaps the original version of the EFI firmware? Or any other suggestions. I have owned this system since new, and other than a Apple hdd replacement 5 years ago and the hdd issue recently it is a great machine.
iMac (27-inch, Late 2009) 2.8 GHz Intel Core i7 16 GB 1333 MHz DDR3 (16GB being recognized) ATI Radeon HD 4850 512 MB
Any assistance, ideas appreciated. Mark Update (05/03/2019) Dan. I used the term broke, because that is what it did. That being said, Apple does this to ensure that “it just works”, I understand why they do it. And despite my searching BEFORE I did the upgrade, a broad search of “Will a Late 2009 iMac 27” i7 run High Sierra?) The results were your usual mix of yes and OMG horrible, etc… But the rationale reviews were positive. Macs have been able to different capacities over and above “Official” Apple specs. As well as variations (speed) of a type ram stick, usually with a little or no improvement, and usually a hit on speed. I did assorted hardware tests on the system (that is how I narrowed the issues i was having to the Hard Drive). Memory was fine, as were all other pieces parts. After the upgrade and ssd install, I ran hardware checks and the memory the iMac could see all came up as good. I did not spend a lot of time initially looking at the ram sticks themselves. Since they all checked out as OK in the assorted tests. Not until i started digging, did i see mentions of the MacOS/firmware disabling what i called sub-standard or approved hardware (like a charger cable, charger, memory, etc. That is when I looked more carefully at the ram stcks, and noticed the “speed” difference. As these were installed at an Apple store, I, again was not super concerned. More research made it evident that while yes the ram sticks were functioning and would most assuredly work great on a appropriately specced machine, these were NOT appropriate for my iMac. So I ordered new Crucial sticks, specced for this iMac. I am not angry, I am disappointed at the Apple store. and Apple for the “fix’, Perhaps i am not tech savy enough to find and read the warnings for upgrades. Which is why I wait awhile before doing these things. I appreciate your input. Mark Advant Memory
Lets, clarify things a bit. As you can see here Install memory in an iMac - 2009 27" iMac So Apple acknowledges it can support it so that’s not the issue. Apple wasn’t stepping on your toes intentionally. They are not checking components/accessories or for sub-standard hardware. Others are not encountering this problem. You do have a hardware problem the question is which side? The RAM you have or the system. As you never supplied any info on the RAM I can’t even check it out. You also didn’t tell us which slots if a given set of slots are failing. So at this point I think you’ll need to find someone locally to help you.
