Model A1418 / Late 2012 / 2.7 & 2.9 GHz Core i5 or 3.1 GHz Core i7 Processor

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Will my SSD work (thermal sensor)?

I have a 2012 21" iMac and I would like to upgrade it's HDD to a Samsung 850 Evo, but I don't know too much about consequences of the upgrade. TRIM might work with the 10.10.4 (although some reports say that Samung SSDs have a problem), but the bigger problem is that I'm not sure the fan would work well. I read about some firmware thing and other iMac owners' experience (all of them have 3.5 HDD) but I haven't found anything about exactly this model. My iMac uses a 2.5 HDD and maybe that makes a difference. So do you have eny experience about this 2012 iMac?

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First I must warn you the newer 'Thin Series' iMac's are a bear to open as you need the correct tools and follow the IFIXIT guides to the letter as any mistakes can kill your display! Which would be an expensive error.

OK, here's the details:

First if you have a Fusion Drive'd system (HD & SSD) you may want to leave things alone here. You will need to break the fusion drive set before you replace the HD with a SSD and you'll need to leave the drives independent.

If you have a HD only system then you may want to look at a SSHD to replace the HD. That way you gain the speed of the SSD the SSHD has for boot up and yet still have a traditional HD for your data.

If you have the bucks then going with a SSD is also possible replacing your HD in the HD only system. But most people find the cost of the larger SSD is prohibitive and tend not to like the system with a small SSD alone (512 or smaller). You may want to think about an external Thunderbolt RAID drive as a better solution.

As to the drive you are correct this system uses a 2.5" drive SATA drive (either HD or SSD will work here). It also has a M.2 type of blade SSD connection which on the back side of the logic board.

As to Samsung SSD's we use them and don't have any problems! You do need to use the newer cut of Yosemite or El Capitan to enable the OS TRIM services.

Follow this IFIXIT guide: iMac Intel 21.5" EMC 2544 Hard Drive Replacement

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Thank you for the answers. I think I will replace my single HDD with the Samsung 850. As you said a normal SSD can be expensive and I must have 500gb of storage but most people say it worth that money. Of course I'm not too experienced with the operation itself but one of my frinds is quite good at this stuff. Steven, I beleive this thermal sensor issue only occurs with the models that use 3.5 SATA.


Yes, the 3.5" drives use a different system. If you can swing it I would go with a larger SSD. Remember you need to leave between 1/4 to 1/3 of the drive free for the OS & Apps caching.


Thank you very much, Dan. 500gb will be enough in my opinion (mainly because the current HDD will work as an external HD and USB 3.0 is fast enough to keep my movies and videos on it). Lastly, do you recommend to enable TRIM (some say it is unnecessary but Apple also enables it for some reason.)?


You'll need to enable TRIM manually as you are using a 3rd party SSD. Apple uses TRIM on their SSD's its just done automatically via the OS. As to TRIM I strongly recommend enabling it. Here's a good writeup on SSD's: The proper care and feeding of SSD storage while its aimed at Windows the core aspects are the same. You'll need to run a command line argument, here is a writeup on how to enable TRIM is OS-X: Latest OS X update allows you to enable TRIM for third-party SSDs


And how difficult this while operation is? I mean I'd like to have the same iMac with no problems. I think I could probably do it myself but I don't want to risk so I have to find someone more skilled. So would you choose a shop specialized for Apple product and pay a lots of money or an average PC store would be enough? As far as I know the remove and the reattachment of the screen are the hardest parts so maybe not every shop has the right tools.


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I have one that's two years older and my fan blared like a jet. I did get "Macs Fan Control" (free) and that tames the fan to normal speeds. I took out the optical drive and installed a Samsung 850 ssd in its place and I must have fried the temp sensor. Anyway, I got the program, I set the fan for a slower speed and I have no problems with it.

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