Using an iMac as a Monitor Is More Complicated Than You Might Think

Using an iMac as a Monitor Is More Complicated Than You Might Think
Image: Apple

If you’ve got an old iMac gathering dust in your home, sitting either on the end of your desk or in the corner of a room, you might be wondering what you can do with it.

Sure, you could sell it, but you could be using it as a second monitor for your laptop or desktop computer.

Here’s how.

How to turn your old iMac into a monitor

So over on the official Apple website, this feature is referred to as “target display mode”. It’s only available with certain iMacs, so if the iMac you want to use as a monitor is of a certain age, it won’t work. You can check the age of your Mac by clicking the Apple symbol at the top of your screen and then “About this Mac”. You can also use Apple’s handy web page on identifying the age of your iMac.

Unfortunately, it’s not as simple as connecting a cable from a computer to a monitor. At the time of writing, target display mode is only available on a handful of iMacs dating back to 2009, with iMacs released after mid-2014 simply not compatible. There are also some strange OS requirements, with more recent macOS releases not allowing access to target display mode.

Check the compatibility of the iMac for monitor use

First, you’ll need to check that the iMac for monitor use meets the requirements for the target display mode. If the iMac is from 2011, 2012, 2013 or mid-2014, then it is compatible, provided that it has macOS High Sierra or an earlier OS installed.

Alternatively, the 24-inch and the 27-inch iMac models from 2009 and 2010 can also be used as an external display, provided that they have macOS High Sierra or earlier installed.

If your iMac is younger than 2014, we’re sorry. It just won’t work.

Check the compatibility of the Mac you’ll be using as the computer

The Mac that you’ll be using as the computer (as in, the iMac or MacBook that will be using the screen of the iMac as a secondary display) will need to be from 2019 or earlier and have macOS Catalina or earlier installed.

What cable do I need for using my iMac as a monitor?

For most setups, you’ll need to use a Thunderbolt or Thunderbolt 2 cable to use the iMac as a display. However, if you’re using an iMac from 2009 or 2010 as the display, you’ll need to connect the devices with a Mini DisplayPort cable.

How to start target display mode and use your old iMac as a monitor

  • To begin, boot up the old iMac and log in with a macOS user account.
  • Once you’ve done this, connect the iMac to the iMac using the appropriate cable (we covered which one you should be using in the previous section).
  • Press Command-F2 on the keyboard of the iMac you want to use as a display. This will transform it into target display mode and will show the screen of the other iMac if all the prerequisite steps have been followed correctly. You can use multiple iMacs as displays.
  • You can disable this mode by pressing Command-F2 again or by disconnecting the cable. Restarting either device also works.
  • Keep in mind that the iMac in target display mode won’t give you access to its built-in camera or ports. If you need to access these, you’ll need to exit out of target display mode.
  • Brightness and sound will, however, be controllable on the target display mode iMac. Accessing Sound settings in System Preferences on the computer-mode iMac will give you control over the monitor-mode screen, and accessing Displays Preferences on the computer-mode iMac will give you control over the brightness on the display-mode iMac.

It’s that simple.

Can I use an iMac as a monitor on a Windows PC?

Yes. Your PC will need to feature the same cable connections as outlined in the earlier section on iMac cables (so Mini Display Port for models from 2009 and 2010, and Thunderbolt or Thunderbolt 2 for iMacs from 2011 through to mid-2014). Alternatively, an HDMI or DisplayPort cable adapter could work.

Just follow the steps outlined in the earlier section, including pressing Command-F2 on the target display mode iMac. This will mirror the screen.

Alternatively, if you want to go really technical, and if you want to use an iMac as a monitor that doesn’t have target display mode, you can turn it into a display through some Boot Camp trickery. Alphr has a guide on this here, however it’ll require a decent internet connection and a Windows PC.