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Proprietary cable can put the brakes on upgrading Late ’09 iMacs.

STOP-hard-drive[UPDATE: No longer is swapping out brand for brand even necessary! OWC has just released the Complete HDD Upgrade Kit with in-line OWC Digital Thermal Sensor for all Apple 2009-2010 iMac 21.5″ and 27″ Models. You can now upgrade your iMac with any brand 3.5″ SATA hard drive. No software hacks necessary and it’s AHT diagnostic compatible.]

Sometimes even the best educated guesses can be thrown for a loop when an unforeseen “X-Factor” comes into play. Such is the case with the Late 2009 iMacs.

As we were getting information together for the new iMac instructional videos, we came across a little tidbit that, apparently, hasn’t been covered anywhere else: Apple has switched the iMac’s method of hard drive temperature sensing. They’ve gone from an external sensor that attached to the outside surface of the drive to a connector that seems to use the drive’s internal sensors.

On first blush, this would appear to be a good thing; an internal sensor is closer to the drive’s mechanics and is likely to be more accurate regarding drive state. Unfortunately, there are no industry standards regarding the ports/pins used to access this information, and each hard drive manufacturer seems to do it their own way. And more unfortunately, when the iMac gets no sensor information via that cable, the heat exhaust fans kick into permanent high gear, so that cable must be connected.

That means, in order to upgrade the internal drive, you need to have a connector cable that’s compatible with the brand of drive that you’re installing… and that’s an Apple service part not generally available to the end user. Pretty sneaky, Apple!

Fortunately, you can reuse the cable that came with your iMac as long as you replace the drive with another model from the same manufacturer we have confirmed works properly with this thermal sensor cable. To determine what brand hard drive your iMac has, go to About This Mac, click on Serial-ATA, and then look for the drive model installed at the factory. If the model has the preface WD, that’s a Western Digital hard drive and if your drive has a ST, that’s a Seagate hard drive. Once you know what drive came with your Mac, you can upgrade to a larger drive and continue to use the thermal sensor…thus avoiding the “ear pleasing” whoosh of fans on high.

Here’s a list of the drives that install into WD factory equipped iMacs.

For the Seagate equipped models, these drives from us will plug right into the thermal cable

Fortunately, upgrading memory is still easy to do, and will show a more immediate improvement in performance than will a hard drive upgrade. That doesn’t mean, though, that somewhere down the road you won’t want to upgrade your hard drive to something larger and/or faster.

We’re all about giving you the most options for upgrading your Mac and that’s why OWC is looking into potential ways to turn this curveball from Apple into a Home Run for you. As soon as we can find a viable method for connecting a different brand hard drive than the one that came with  your 2009 iMac,  you can be sure you’ll hear it first right here on the OWC Blog.

In the meantime, if you get stuck for storage, you can always take advantage of that lone FireWire 800 port (or, if necessary, one of those USB 2.0 ports) and add a fast external storage device, such as the Mercury Elite-AL Pro. The benefit of this is that when you are able to upgrade that internal drive to your preference, you will have a handy extra external unit for backing up to.

Keep tuned to the OWC Blog for updates…

Related Post: Diagnosing 2009 & 2010 iMac Fan Speed Issues After Upgrading The Main Hard Drive

NOTE: The comments on this post have been closed. For more information, please read our latest update on the Rocket Yard.

OWC Chris S.
the authorOWC Chris S.
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  • Hi I have a big problem bought a newSeagate Barracuda 3 TB ST3000DM001
    installed it into hard drive bay replacing the WD caviar 500gb in my 2011 imac 21 inch, Installation no problem,When I boot up I am met with the folder and flashing question mark symbol .When i place the new drive back into an external caddy it is fine boots up with Yosemite with hdd control on it also, so there is a boot partion,
    can anybody help me with this please I’m scratching my head with this

    • You can get around the need for the HDD Fan Control with our thermal sensor cable.

      Was your original drive having this same issue? If so it could be your internal SATA connection at fault. With the new HDD installed, I would try both a SMC and a PRAM reset.

      SMC reset: http://support.apple.com/en-us/ht3964


      PRAM Reset:
      1) Start the machine while holding down the Option-Command-P-R keys

      2) Wait until you hear the 3rd startup chime, then let go of the keys and let the machine boot up.

    • Hello Marko,

      The late 2009 21″ iMac does not have a SSD bay. It only has 2 SATA ports 1 for the main drive bay and 1 for the optical drive bay.

      We offer an adapter for you to replace your optical drive with a 2.5″ drive – http://eshop.macsales.com/item/OWC/DDIMCL0GB/. We also offer a kit to replace the drive in the main bay – http://eshop.macsales.com/item/OWC/DIYIMACHDD09/. If you were installing our Electra 6G SSD into the main bay you’d also need this 2.5″ to 3.5″ drive adapter -http://eshop.macsales.com/item/NewerTech/ADPTADRV/

      • Hi Ben,

        Thanks for quick respond. I already ordered the Electra 6G SSD from your site, I expect it to arrive in next 10 days, but I thouhgt that there is a space under the optical drive and did’t consider that there is no other connection for 3rd drive ;)
        Than I must install it instead of optical drive. Do I need the adapter or I can use double sided tape to fix it on optical drive housing?
        Many thanks…

        • You’ll need the adapter because the optical bay uses a micro SATA connection and the Data Doubler has the micro SATA to SATA adapter necessary to use the Electra drive.

  • So does this mean we are still stuck with Hybrid drives? I really want to upgrade my late 2009 Imac with a SSD. Is there no OWC SSD drive that I can use, that will avoid the fan issue?

    • I’m sorry, because of the proprietary compatibility of those connectors to the brands of the drives, we do not carry any SSDs that connect with the stock temperature sensor in the late 2009 iMacs at this time. Please keep an eye on our blog or subscribe to our newsletter for any potential announcements of products that may be compatible in the future.

    • Yes, you CAN replace the 3.5″ SATA stock drive with a SSD from OWC (just did it yesterday), but you need to run 3rd party software to prevent the fans from kicking into full speed (6000rpm). Below are the 3 I’ve used, first one costs a little $ (good dev) and last 2 are free. They allow you to control the fans based in internal temp or S.M.A.R.T. temp. :)

      1) http://www.hddfancontrol.com
      Free 1 hour trial, then paid. I’ve had good success with this one.
      Quantity Price
      1 – 4 $35.00
      5 – 9 $20.00
      10+ $15.00

      2) http://exirion.net/ssdfanctrl/
      I’ve used this one as well… great software for FREE

      3) http://www.crystalidea.com/macs-fan-control
      new one I’m trying out

  • Hi, I’ve got a 21.5 imac late 2009, it had a 500gb seagate hard drive I have replaced it with exact same model as the previous one failed on me, I’ve put the thermal sensor correctly as before it would spin furiously now it builds up slowly and then stays fast, I’ve tried everything as everything else is east same as I replaced model for model but fan is still spinning all the time, it’s driving me nut, please help! Thanks

    • Sorry to hear about the trouble. It is best to follow our steps in this blog to see which fan is causing the problem. It may not be the HDD fan, another sensor might have been knocked loose or pinched.

  • I have an iMac late 2009 with i7 2.8GHz. The internal Seagate 1TB HDD died. Unfortunately I have not been aware of the free replacement program that Apple used to offer, so I decided to replace it with a new one. Could I replace it with a Seagate hybrid drive, such as ST2000DX001?

      • Fans and Temperature sensors will work exactly the same as with the stock drive? No special apps required to control fan speed with that Seagate Hybrid? It can be used as a drop-in replacement, in the stock HD location?

        • That is correct if your 2009 iMac originally came with a Seagate drive. If it came with a Western Digital or Hitachi drive they would need to match those brand drives.

          • Really? I too have a I have an iMac late 2009 with i7 2.8GHz, albeit with a Western Digital HD 1TB. If what you say is true (that we can only replace Seagate with a Seagate, a WD with a WD, or a Hitachi with a Hitachi), that would mean Apple made 3 different HD interfaces for that late 2009 i7 iMac, right? But why would they do that? Why not make a single HD interface that works with all 3 drives they intend to use in that iMac model? Why make 3 incompatible interfaces?

            • Correct, but only the “heat sensor” cable/connector is different for the 3 brands of drives (Toshiba is made by Hitachi FYI, WD, and ST). So Apple has 3 different heat sensor cables. The SATA and Power cables are the same for all drives and iMac models (2005+).

  • I did not see this post before ordering a new drive…so I am experiencing the “permanent high gear” scenario. The problem is this: the original HDD in my 21.5″ 10,1 iMac is a Hitachi HDT721050SLA360. What do you have for a replacement option? My temp. sensor connector is a 2-pin version, and it is a different shape/size than the Seagate drive I bought to replace it. Suggestions?

      • Hi Shawn, the drive would be compatible if it is a Hitachi drive that you removed. Please contact our tech support team via phone at 800-869-9152, or 815-338-8685 internationally; by chat; or by e-mail if you have any questions.

    • I am in the same position as you, did you ever find out what drive replaces the Hitachi and has a 2-pin connector?

  • I am working on a 27in iMac 11,1 (2009). It had a seagate 1TB drive, and therefore the seagate cable. Per talking with one of your techs, I found this info, but no luck.

    The original drive (which is dying) is a 1TB barracuda, the replacement is a 500GB seagate Constellation. They have the same 4 pin connector for the temp sensor, but the fans spool up anyway. Using a temperature monitoring utility the drive is reported at about 33C but another sensor reports 9C and the fans spool up to near max.

    Unfortunately I do not have another barracuda in house to test, everything else in the shop is WD and uses a different sensor cable, which I do not have time to order.

  • WD2003FYYS ( Frys ) vs. WD2003FZEX ( suggested )

    I have a Apple iMac “Core i3” 3.06 21.5-Inch (Mid-2010) and Frys has a similar model to the one you suggested.

    Are they compatible ?

    Thank you in advance

    • All our testing has shown that replacing a stock drive with one of the same brand should work without any trouble, so if your original, factory installed drive is Western Digital then either of those drives will work.