Upgrade the Hard Drive in 2009 and Later iMacs

Keep Your iMac Cool With an In-Line Temperature Sensor

iMac open for repair
Courtesy of Pixabay

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.

Update:

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.

Should You Decide to Upgrade Your iMac's Drive…

The process of upgrading an iMac's storage system involves accessing the iMac's internals. Getting inside involves removing the computer's display in order to gain access to the iMac's internals, including the hard drive.

Apple has changed how it attaches the display to the iMac's chassis over the years, resulting in two very different methods of removal.

2009 Through 2011 iMacs

The glass display is attached to the iMac chassis using magnets, and no, these aren't mystical glass magnets.

The display's glass panel includes embedded magnets that adhere the glass to the iMac's chassis via magnetism. This simple method of attachment allows for a simple method of removal, using two suction cups to pull the glass away from the chassis, breaking the magnetic seal.

Once the display panel's seal is broken, the display can be easily removed by disconnecting a few cables. Once the display is set aside, the Mac's internals, including the hard drive, are exposed, and drive replacement can proceed.

2012 Through 2015 iMacs

In 2012, Apple changed the design of the iMac models to produce a thinner profile.

Part of that design update changed how the iMac's display was attached to the chassis. Gone are the embedded magnets in the glass; instead, the glass is now glued to the chassis. This allows for a thinner profile and a higher display quality since the display and glass panel are now fused together, resulting in a crisper display with a higher contrast ratio.

The downside is that in order to remove the display, you must now break the glued seal, and just as important, you have to re-glue the display to the chassis when you're done upgrading the iMac.

I mentioned before that upgrading the iMac models was a difficult DIY project; for the 2012 and later models, it has an even higher level of difficulty.

Drive Replacement

Before you consider a drive replacement on a 2009 or later iMac, I recommend viewing the teardown guides at iFixit for your particular iMac model, as well as the install videos at Other World Computing (OWC) to see step-by-step guides to replacing your iMac's hard drive.

SSD Replacement

Your hard drive isn't the only DIY project you can perform once inside your iMac. You can replace the hard drive with a 2.5-inch SSD (3.5-inch to 2.5-inch drive adapter required). In 2012 and later models, you can also replace the PCIe flash storage module, though this involves almost a full disassembly of all internal components, including removing the power supply, hard drive, logic board, and speakers, as well as a few odds and ends.

By the time you've completed the PCIe flash storage upgrade, you would have rebuilt your iMac almost from the ground up.

As you can imagine, I don’t recommend this last upgrade, but for those of you who enjoy extreme Mac DIY, this may be a project for you. Be sure to review the iFixit and OWC guides mentioned above before you decide to tackle this project.