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iMac Hard Drive Upgradeability Expanded!

As you may recall, Apple changed the hard drive upgrading game with the  2011 iMac.

Up until 2009, changing a drive was easy once you could get to it. A few screws here, a connector there and voila – you were good to go. And OWC had you covered for all your iMac DIY hard drive upgrades.

With the late 2009 iMacs, Apple introduced a different connector for each brand drive, but as long as you stayed within the same hard drive brand, then it was the same, once you got to it – it was easy-peasy to make the old switch-a-roo. And OWC had you covered for your iMac DIY hard drive upgrades.

Then came the 2010 iMacs and the ‘same for same’ caveat still applied, but the 27″ iMac model introduced an additional SATA drive connection on the motherboard and the OWC Turnkey Upgrade program was born. Send us your 27″ iMac and we’d add up to 3 SSDs or even an eSATA port. It was a little more difficult, so we started with a do-it-for-you service, then made it available as a DIY kit. And OWC had you covered for all your iMac  DIY hard drive upgrades.

Lo and behold, the 2011 iMac changed the game again, no longer could you swap out the drive without failing the Apple Hardware Test (AHT) and sending the fans into a tizzy. Soon after, we expanded the iMac Turnkey Program with our Do-it-for-you service on these machines as well. And, now, we’re happy to announce that we’ve crafted that solution into an elegant little DIY Kit. So, once again, OWC has you covered for all your iMac DIY hard drive upgrades.

(OK, ok – we’re still working on the late 2012 iMac drive options, and – please – give us a little more time there. Apple changed it up again going to the new form factor iMac with a blade-style SSD.)

So how did we do it? 

Well first, a little background on what the issue is exactly, and what is the proper way to solve it…

Apple introduced a firmware element to hard drives that are factory-installed which allows the drive’s internal temperature monitoring system to communicate with the System Management Controller (SMC) which controls the power functions, battery, the sudden motion sensor, the fans, and other functions. When the SMC doesn’t receive temperature data it expects,  it goes into failsafe mode directing the fans to rev to full speed and further reporting drive sensor failure via Apple Hardware Test.

When installing a hard drive that lacks the special Apple firmware, the SMC goes into failsafe mode since it is no longer receiving data on what the drive temperature is. The fans then rev to max on the basis that a drive is in the bay and it wants to ensure protection of the drive regardless of load on the drive and heat level from ongoing loads.

There have been several forums and blogs that offered workarounds to this situation, but these hacks weren’t optimal:

Some sites suggested shorting pins in the power cable or drawing power from another drive bay so the drive no longer would be expected to report temperature information at all. But allowing the drive to get too hot can easily cook a drive.

Others suggested to use 3rd party software to to manually control fan speed.  This software is not free nor an ideal solution as you run the risk of overheating if mis-configured or disabled by accident, software update, or OS re-installtion.

Simply put, lack of active heat monitoring could lead to a drive failure.

What is the solution for the 2011 iMac, then?

The OWC HDD kit provides a cable with a digital thermal sensor module that is able to ‘talk the same talk’ with the SMC. By replacing the stock Apple cable, the SMC is no longer relying on the Apple firmware for temperature data.

Use of this kit allows the installation of any standard 3.5″ Serial ATA hard drive with capacities now up to 4.0TB. With the included custom cable, the HDD bay has proper thermal monitoring communication, the iMac will pass AHT testing, and the HDD bay will be properly cooled per Apple settings just like the original factory drive. In short – an optimal solution for your 2011 iMac hard drive upgrades.

While you’re in there – you’ve got a great opportunity to consider upgrading or adding an SSD for a super performance boost. The OWC SSD kits make that easy too. And if you purchase one of our full kits, you can buy just the support kit (without the tools) for the 2nd upgrade portion.

Finally, don’t forget memory – most systems shipped with only 4GB of memory and with today’s modern Operating Systems – there are benefits for having up to the 32GB maximum the iMac 2011 models support. With 4 slots for memory and only two typically occupied from the factory – it’s easy and provides a night and day performance boost for many applications when you add even just another 4GB, 8GB, or 16GB to that existing memory.

We even walk you through, step-by-step on how to perform each of the above the upgrades in our Installation videos for the 2011 iMac models.

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  • I installed a 5tb WD Black sata and the OWC upgrade kit on my Mid 2011 iMac and mine has ALWAYS ran super HOT!!!! Now the hard drive is really loud making buzzing type noises… :-(

    • Thank you for sharing this Jeremy. We are reaching out to you now to speak with you further.

  • I replaced my OE HDD on my mid 2011 21.5″ iMac with a WD 5TB with all the heat sensor accessories. Runs GREAT… BUT the HEAT from the HDD is so hot it will BURN you! How can I fix this problem? It was happening BEFORE I upgraded to Sierra. Previous OS 10.8.6

  • Hi. I have a 21.5″, late-2012 iMac 13,1. The original drive failed and I ordered and have replaced it with an OWC 480TB SATA SSD. Now my CPU utilization is 180 percent. Is there a sensor kit for this iMac?

  • I have a mid 2010 iMac 27″
    The hard drive has failed so need replacing

    Would ideally want to do a straight swap out with a 1tb HDD

    What did i need to order
    Have been told a 1TB WD Black WD10JPLX will do but worried about the fan issue

  • Wanting to know if I can use a 3tb drive out of an early 2009 Imac27 and put it in a 2011 or 2012 imac27. Does it slot straight in or do a knee an adaptor kit if so which one
    Thanks Pete

  • Hello!

    i’m gonna replace my HDD on my iMac late 2013 21.5 inch model (2.7 i5) and I have some questions.

    1. Do I need these thermal things? I can only find info about the 27 inch model.

    2. What is the connector to the HDD in this iMac model, does this SSD fit in that connector? (The SSD: )

    3. Are there any other cables/comverters etc. needed for the replacement of the HDD?

    • Great questions! In the late 2013 iMac you will not need any sort of thermal cables or extra cables. All you will need is to put any 2.5″ SATA SSD in place of the original HDD. The SSD that you listed is compatible but we would recommend taking a look at the OWC Mercury Electra and Extreme SSD.

      If you have any further questions, please let us know!

      • So the fan will not run at full speed? I mean by default the fan will run at full speed if the logic board doesn’t get info from the thermal cable. Or isnt that an issue with this model?

      • So I don’t need any software to control the fan? Ive read that the fan will go a max speed when the logic board dont get info from the thermal sensor.

        • Hello Albin,

          You will not need any software or extra hardware in order for the fans to run properly. The late 2013 21.5″ iMac does not have the thermal problems.

          Please let us know if you have any further questions!

  • I have a client with this system listed below and has a full HD. I want to upgrade her to a 2 TB drive if possible. After reading your notes and on some other sites, I decided to seek your help and buy a DIY kit if needed. Here are the specs of the system:
    purchase date on my Mac 1/3/11
    iMac 21.5 inch, Mid 2010


  • I have a March 2009 24″ imac. Can I put any drive in it and will I have any issues. I want to put either a hybrid drive or a 4tb but don’t want the fans to go crazy

  • I have 2011 iMac 12,1 with dead HDD. Bought the 1.0 Tb Seagate Desktop from your website (couldn’t find a 1.0 T Seagate Barracuda to match what’s in the Mac), and bought installation kit.

    After successful installation per your vid including your supplied thermal sensor connector, I have continuous running fan. Driving me nuts. Had to take the drive and sensor out.

    Wrong drive for this mac? Does the OWC sensor only work with the SSD? Is eternal spinning fans to be expected with your product? Thanks for any help.

  • So, I’ve upgrade the drive using the OWC kit, replaced the cable etc. Great video etc. But, now how do I install a new Yosemite OS on the drive OR format it properly? Can’t find any details anywhere for this final process. In the meantime, the iMac mid 2011 starts up with a blinking folder and a question mark. HELP!!

  • Hi, I bought an OWC 2011 27inch imac hdd kit a while ago but My cables are different the cables being distributed not. I have the one that is pictured in this blog post. I only have one black long cable and a small white cable that I dont know where it goes; as well as the thermal chip. Did I just buy the wrong one? I couldnt find any ideo tutorials that uses the cables THat I have now.

  • I have a 2011 27″ iMac. After following the instructions to add the ssd behind the optical drive, is there any harm in removing the primary hdd and leaving that spot empty?

    • Hello Terry,

      There would not be any issues leaving the main HDD bay open. It is recommended to keep the original HDD in for a back up or extra space.

  • I have an iMac 21.5″ (Late 2013), I want to upgrade the Hard drive to a 1 TB SSD, Which thermal Sensor Cable do I need or do I need, and what else would I need?

    • In the Late 2013 21.5″ IMac you will not need a thermal cable. This computer comes with a standard 2.5″ drive so you will not need any adapters. The only thing you will need is a 2.5″ SSD and it will be a direct fit!

      • So no interference with SMC with – lets say – a 2,5″ samsung 850pro ssd?

        No fan-control needed?

        • In the Late 2013 21.5″ iMac, there will be no problems upgrading the drive. There will not be any fan control problems or thermal issues!

  • I can’t believe I don’t find any comments of someone trying to install the thermal sensor in a 2011 21.5″ imac. I tried it today. The cable, OWC sells as compatible with all 2011 models, does not fit. There is no room for the cable. The video of the installation is been done in 27″ imac. Where there is plenty of room next to the hard drive to store away the cable. I am curious if anyone succeeded installing this thermal sensor cable in a 21.5″ imac.

    • Installed the inline thermal sensor in mid-2011 21.5″ iMac. Yes it’s tight but you can push the cable under the metal bar at the rear of the drive.

  • Hi,
    I installed this on my mid 2011 27″ iMac and the graphics card is not working now.
    Any ideas?

  • Hello – I have a late 2009 iMac which even after adding additional memory to 16GB the computer no longer plays movies or TV show properly. There seem to be a lag or delay a short time into the play back and ultimately the voice/picture become out of synch. I am running Yosemite….but I wondered if you might have any suggestions? Thanks much.

    • Hello Rick,

      I would suggest to check your internet connection speeds. If you are experiencing lag when playing movies or TV shows from the internet, the connection could be weak or not fast enough.

      If you are experiencing lag when using a DVD, CD, internal or external drive, I would suggest to run a PRAM and SMC reset.

      If this problem still persists, please contact our Tech support team and we will be happy to troubleshoot this with you.

  • I installed an OWC Mercury SSD with Temperature cable in my Mid 2011 iMac. Once I installed the OS (Yosemite) the computer no longer sees my internal monitor. Only my external. Prior to installing the Yosemite, the monitor fired up with the gray screen and question Mark.

    • We are sorry to hear about the SSD troubles. I would recommend to start with a SMC reset and a PRAM reset.

      If this problem still persists, please contact our Tech support team and we will be happy to troubleshoot this with you.

  • 7 TB IMAC I7 UPGRADE . In relation to installing new hard drive( 2011 i7 27″ ) & placing solid state drive behind the ODDrive.Just for information a few days back I replaced the original 1TB Seagate drive with a 6 TB WD green and placed a 1TB Samsung behind the optical bay. I used the OWC kit for each. I am not an expert and it was the first time I have attempted iMac surgery, I must say it was easier than suggested but watched the OWC videos about 20 times first.. Secondly just to be safe I have also purchased the Tunabbelly temperature gauge app which gives 28 different temp sensor readings. This appears to to be very useful as I can see other readings such as the power supply which can be a great source of heat in an iMac 2011 . I ran it for a few days but as I am unaware of the true temp parameters for things other than the hard drive I have also installed the HDD fan controller software which seems quite flexible in adjustment parameters. Before using HDD the fan was not running too fast but just in case something else was causing excess heat i thought it better to play safe and use HDD as an extra precaution. I don’t know of any one on the net with a 7 TB combined drive to date. I have 2 X 16 TB Promise Back ups for my photography but was forced to increase my internal & would nearly fill the new 8 TB but will install that lf all goes well here . I failed to say in my last post it is running super fast all seems well . My only questions is waht is the normal operating temp for the power supply? as this is seems to get up to around 70 C after several hours of use or when using heavy applications ? I would to have all the normal temperture parameters for this model mid 2011 if anyone can help ? The Tunabelly gauge app lists 28 odd deferent readings but just the main ones would be good. Its all running fine with a few twigs of the HDD app for the extra cooling. Let me know how you went with a similar project.

  • Hi, Upon installing of new 3TB WD Black HD and OWC In-line Digital Thermal Sensor for iMac 2011 HD Upgrade, the Apple HW Test fails. I’ve got a mid 2011 iMac (12,2) and latest Mavericks OS. Tried asking OWC tech support but they couldn’t figure out why would it fail the test either. I’ve tried SMC/PRAM resets and replace the HD with Seagate and WD Black HD 4TB drives. I tried 2 cables from OWC. Could this be bad cables? Please help. Thanks.

    • I went through 5 cables, following install exactly. After opening the casing a couple dozen times, checking every single cable, I put the original cable and downloaded the following. Wish I would have done this from the get go. It’s the only free program that let’s you set maximums, and it works in bootcamp.

  • mid 2010 21.5 imac – any issues with going to 4tb? specifically looking at the 4tb: seagate sshd STCL4000400

    • We unfortunately do not have a DIY kit to replace the main drive in the 2010 iMacs. We recommend replacing the existing drive with the same exact brand to avoid any thermal issues. A 4TB drive of the same brand shouldn’t have any issues.

  • On a SSD, where should the sensor be placed for best/safest performance ?

  • Hi,

    I have a late 2009 27in iMac. Apple did the Samsung 1 TB harddisk replacement, but since then I have the problem that the monitor keeps going to sleep. It can be every 2 minutes, or it can be 3 days till it happens, but happen it will.

    The Mac is running, I can see the desktop dimly when I shine a light on it, and by making the bottom right corner activate the screen saver I can get it back to working by moving the mouse to the bottom right corner and out again, thereby activating and deactivating the screen saver.

    Any idea where the problem might be? It doesn’t seem to be temperature related. After reading this page I wonder if Apple put a “not completely compatible” drive in …

    Thanks for any advice.


    • I had this same issue on my 2008 24″ iMac. The LCD backlight is the specific item going out. It generally is not heat related, it is just one of those parts that will eventually go out on a display. I would recommend taking it to the Apple store that did the hard drive replacement. Since they looked at it somewhat recently they might be willing to take a look at it for you. You can also take it to an Apple authorized repair center. We do also offer repair services here, you can contact our customer service at 1-815-338-8685 to get a quote for diagnostics and repair.

  • I have a mid 2010 iMac and want to upgrade to Seagate SSHD what cable should I bye to support thermal sensor.

    • For the 27-inch 2010 iMac, you can add any brand SSD (although we do highly suggest the OWC brand) with our DIY Kit. This installs the SSD in addition to the internal hard drive, not instead of.
      If you have a 21-inch model, then the main hard drive bay is all that is available. In either model, to replace the main hard drive, you do need to swap it with another same-brand (although it can be a higher capacity) 3.5″ HDD as originally installed.

      • G’day, for a 27″ iMac’s HDD mid-2010 with a 2TB Hitachi HDS722020ALA330, what new (e.g. 4TB) HDD can I replace it with? I am also thinking about adding a SDD where I would put the applications on.

        about “… in either model, to replace the main hard drive, you do need to swap it with another same-brand (although it can be a higher capacity) 3.5″ HDD as originally installed….”

        Hitachi Global Storage Technologies aka HGST was founded in 2003 as a merger of the hard disk drive businesses of IBM and Hitachi.
        In 2012, Western Digital (WD) acquired HGST

        The fan control issue is both a physical connection and a firmware issue, it seems. Besides Apple, does anyone sell a HDD with the correct connection for the current temperature sensor as well as the required firmware so the fan doesn’t go crazy? Or, another hardware solution (not keep on a software override fix)


  • We need to replace hard drive in a 27″ 2011 iMac. I have the SSD picked out and the mounting bracket as well.
    Do I need the Custom iMac HDD power cable with an in-line digital thermal sensor module as well and if so is it compatible with SSDs?

    Thanks so much! -C

  • My late ’09 died so I pulled the drive. Any way of getting the data off it. I have a Stardock Sata / IDE external unit but no adapter cable. Any thoughts? I can’t be the only cat eatin’ Cheetos here… BTW is that a standard SATA connection with altered pinouts? I’ll keep researching. I’ve been doin’ this stuff since the eighties and darn if I ain’t tired of chasing the techno devil! Tell me how simple this really is!

    TIA – Barry

      • Thanks! I awoke about 3 AM under that assumption and went to insert it into my StarDock. The mounting pins swaged into the drive mount holes precluded that…
        Non standard…grrr.

  • Hi.
    I purchased the OWC HDD KIT and I put a 3TB Seagate Hard Drive (I put an SSD 128GB also)
    The installation was perfect. I did the fusion drive, restored from a Time Machine Copy and all went perfect…
    But the fan of my hard drive is spinning too fast. It begins slowly but the speed is increasing until is very high.
    Am I missing something? Do I have to reset the SMC?, Time Machine restoration is not recommended?, Fusion drive?
    Maybe the temperature sensor is not working?


    • We are sorry to hear about the fan trouble. I would recommend to start simple with doing a SMC Reset and a PRAM Reset. If the issue persists the thermal sensor will need to be checked to make sure it is firmly attached to the HDD. If the sensor is firmly attached to the HDD and the fans are still running on high please contact our tech support for additional support, a replacement cable may be needed.

    • did you ever find a solution for your cable problem? i have gone through 3 cables already and still trying to figure it out. original hard drive and cable work fine so i know it’s not a different cable issue.

  • I am thinking about purchasing a preowned 2011 iMac. I would like to do the following:

    Upgrade to 16 GB
    Upgrade to from 1TB HD to 120GB SSD (I have NAS and do not need the storage)

    From reading this article here is what i believe i need:

    If i plan to mount the SSD where the original HD resides will i also need a mounting kit? I would prefer not to mount it in with Tape

  • I have a late 2009 iMac 11.1 rev
    it has a Western digital 1TB drive WDC WD100FALS-40U9B0 and the imac has a Intel 5 series chipset
    I want to install a SSD and or a 4TB hdd
    what are my options?

    I have read tha apple has made upgrading these drive an issue .. Thx

  • I am glad to here that you are still working on upgrading the late 2012 iMac’s. I thought maybe you had given up on those.