Archive for November 25th, 2016

by Tom Nelson

Upgrading the hard drive in an iMac is a DIY project that has always been a difficult, though not impossible, task. With the advent of the late 2009 edition iMacs as well as all subsequent iMac models, there’s a new twist that limits how you can upgrade the iMac’s hard drive.

iMacs have always had a temperature sensor for their internal hard drive. The Mac operating system monitors hard drive temperature and adjusts the internal fans to ensure optimal airflow to keep the hard drive, as well as the rest of the iMac’s inner workings, cool.

Up until the late 2009 model iMacs, the temperature probe for the hard drive was mounted to the hard drive’s cover. When you upgraded the hard drive, all you needed to do was to re-attach the temperature sensor to the new hard drive’s case and you were ready to go.

That changed with the 2009 21.5-inch and 27-inch iMacs. The temperature sensor that was attached to the external case is gone. In its place is a cable that connects directly to a set of pins on the hard drive, and reads the temperature from the temperature probe that is built into almost all hard drives. Sounds like a better system, and it is, at least as far as gathering accurate temperatures from the iMac’s hard drive.

The problem is that there is no standard for which pins to use on a hard drive for the temperature sensor. In fact, the cable Apple uses must be custom made for each brand of hard drive Apple puts in the late 2009 iMacs.

For the end user, this means that if you decide to upgrade the iMac’s hard drive yourself (something we don’t actually recommend for the average user), you can only use a hard drive from the same manufacturer. If your iMac came with a Seagate drive, you can use only a Seagate drive for a replacement.
Likewise, if it came with a Western Digital drive, you can only replace it with another Western Digital drive.

If you use a drive from a different manufacturer, there is a very good chance that the temperature sensor will not operate. In order to compensate, your iMac will set its internal fans to the maximum RPM, creating a nerve-wracking noise that will not be pleasant to be near.

Our thanks to OWC (Other World Computing) for sharing this discovery.


Internal SSD DIY Kit for All Apple 27-inch iMac 2011 Models. Image courtesy of Other World Computing.


Thanks to our friends at OWC, there is now a DIY kit for upgrading a hard drive in an iMac that includes a universal temperature sensor. This temperature sensor will work with any brand of hard drive or SSD, allowing you to choose the best drive that meets your needs without having to worry about runaway fans in your iMac.

Read more on Lifewire: Macs.

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