Turn Your iMac Into an External Display: A Comprehensive Guide
Ever wished you could expand your workspace without buying a whole new monitor? If you have an older iMac lying around, you might be in luck! You can actually use certain iMac models as an external display for another computer, like a MacBook, PC, or even another Mac. This is a fantastic way to repurpose older hardware, boost your productivity, and enjoy the iMac’s beautiful screen for other tasks. This comprehensive guide will walk you through everything you need to know, from compatibility checks to troubleshooting common issues.
Why Use Your iMac as an External Monitor?
Before diving into the how-to, let’s explore the benefits of using your iMac as a secondary display:
* **Cost-Effective:** Instead of buying a new monitor, you can utilize existing hardware, saving you money.
* **Eco-Friendly:** Repurposing old technology reduces e-waste, making it a more sustainable option.
* **Increased Productivity:** A larger screen real estate allows for better multitasking and organization of your workflow.
* **High-Quality Display:** iMacs boast excellent screen quality, offering vibrant colors and sharp resolution.
* **Declutter Your Desk:** Consolidate your setup and minimize the number of devices on your desk.
Compatibility Check: Which iMacs Can Be Used as External Displays?
Not all iMacs support being used as external displays. Apple’s Target Display Mode feature, which enables this functionality, is only available on specific models. Here’s a breakdown:
**iMacs that *CAN* be used as external displays:**
* **27-inch iMac (Late 2009 and 2010):** These models support Target Display Mode via Mini DisplayPort.
* **27-inch iMac (2011, 2012, 2013 and Mid 2014):** These models support Target Display Mode via Thunderbolt.
* **21.5-inch iMac (2011, 2012, 2013 and Mid 2014):** These models support Target Display Mode via Thunderbolt.
**Important Considerations:**
* The *target* iMac (the one being used as the display) *must* have macOS High Sierra or earlier installed. Target Display Mode was discontinued by Apple after High Sierra. This is a crucial point often overlooked. You cannot use Target Display Mode on an iMac running Mojave or later. To confirm your iMac’s macOS version, click the Apple menu in the top-left corner and select ‘About This Mac.’
* The *source* computer (the one sending the video signal) can be running a more recent operating system. However, compatibility may vary, so testing is recommended.
**iMacs that *CANNOT* be used as external displays:**
* Any iMac released after Mid 2014. These models lack Target Display Mode functionality.
* Any iMac with a 24-inch screen size.
* Any iMac with a Retina display. While these displays are beautiful, they don’t support Target Display Mode.
* iMac Pro: These machines also do not support Target Display Mode.
**How to Identify Your iMac Model:**
1. Click the Apple menu in the top-left corner of your screen.
2. Select “About This Mac.”
3. In the window that appears, you’ll see your iMac’s model name and year. For example, “iMac (27-inch, Late 2013).”
Once you’ve identified your iMac model and confirmed its compatibility with Target Display Mode, you can proceed to the next step.
What You’ll Need
Before you begin, gather the following items:
* **The Target iMac:** The iMac you’ll be using as the external display (running macOS High Sierra or earlier).
* **The Source Computer:** The computer you want to connect to the iMac (e.g., MacBook, PC, or another Mac).
* **A Compatible Cable:** This depends on the iMac’s model:
* **Mini DisplayPort:** For 27-inch iMacs (Late 2009 and 2010).
* **Thunderbolt Cable (Thunderbolt 1 or 2):** For iMacs (2011 – Mid 2014). *Crucially,* this is *not* the same as a USB-C Thunderbolt 3 or 4 cable. You need a genuine Thunderbolt 1 or 2 cable, with the distinctive Mini DisplayPort-like connector.
* **Keyboard and Mouse (for the Target iMac):** Needed to boot up the target iMac and potentially troubleshoot.
Step-by-Step Instructions: Setting Up Target Display Mode
Here’s how to connect your iMac as an external display:
1. **Power On Both Computers:** Ensure both the target iMac and the source computer are powered on.
2. **Connect the Cable:** Connect the appropriate cable (Mini DisplayPort or Thunderbolt) between the two computers. Plug one end into the corresponding port on the target iMac and the other end into the appropriate port on the source computer. Make sure the connections are secure.
3. **Initiate Target Display Mode on the iMac:** There are two ways to activate Target Display Mode on the iMac:
* **Using the Keyboard Shortcut:** Press **Command (⌘) + F2** on the target iMac’s keyboard. Sometimes, you may need to press **Command (⌘) + Fn + F2** depending on your keyboard settings. The iMac’s screen should switch to display the output from the source computer.
* **Using System Preferences (if the keyboard shortcut doesn’t work):**
* On the target iMac, go to System Preferences > Keyboard > Shortcuts.
* Click on “Display” in the left sidebar.
* Make sure the box next to “Turn Target Display Mode On or Off” is checked, and verify the keyboard shortcut. If it’s not checked, enable it.
* Try the keyboard shortcut again.
4. **Adjust Display Settings (on the Source Computer):**
* On the source computer (e.g., your MacBook), go to System Preferences > Displays.
* You should see the iMac as a detected display. You can now configure its settings, such as resolution, arrangement (position relative to your main display), and mirroring options.
Troubleshooting Common Issues
Even with careful setup, you might encounter some issues. Here’s how to troubleshoot common problems:
* **iMac Not Recognizing the Source Computer:**
* **Check the Cable:** Ensure the cable is securely connected to both computers. Try using a different cable to rule out a faulty connection.
* **Verify Compatibility:** Double-check that your iMac model supports Target Display Mode and that you’re using the correct cable type.
* **Restart Both Computers:** Sometimes a simple restart can resolve connectivity issues.
* **Check macOS Version:** Make absolutely sure that the *target* iMac is running macOS High Sierra or earlier. This is the most common reason for Target Display Mode not working.
* **Keyboard Shortcut Not Working:**
* **Try Fn Key:** As mentioned earlier, try pressing **Command (⌘) + Fn + F2** instead of just **Command (⌘) + F2**.
* **Check Keyboard Shortcuts:** Go to System Preferences > Keyboard > Shortcuts > Display and ensure the Target Display Mode shortcut is enabled and correctly configured.
* **Test with a Different Keyboard:** If possible, try using a different keyboard to rule out a keyboard issue.
* **Display Quality Issues (Resolution, Colors):**
* **Adjust Resolution:** On the source computer, go to System Preferences > Displays and adjust the resolution of the iMac display to the desired setting. The native resolution of the iMac is usually the best option.
* **Calibrate the Display:** Use the Display Calibrator Assistant (System Preferences > Displays > Color > Calibrate) to fine-tune the color settings.
* **Check Cable Quality:** A poor-quality cable can sometimes cause display quality issues. Try using a higher-quality cable.
* **iMac Freezing or Crashing:**
* **Check System Resources:** Ensure the iMac isn’t overloaded with other applications running in the background. Close any unnecessary programs.
* **Reset SMC:** Resetting the System Management Controller (SMC) can sometimes resolve hardware-related issues. The procedure for resetting the SMC varies depending on your iMac model. Search online for instructions specific to your iMac.
* **Reinstall macOS:** As a last resort, consider reinstalling macOS on the target iMac. This can resolve software conflicts that may be causing the issue.
* **Lag or Slow Performance:**
* **Close Unnecessary Applications:** Make sure the source computer isn’t running too many demanding applications at the same time, as this can affect performance.
* **Check Network Activity:** High network activity on either computer can also cause performance issues. Close any unnecessary network-intensive applications.
* **Upgrade Hardware:** If the source computer is underpowered, consider upgrading its RAM or processor.
* **Thunderbolt Port Issues (Source Computer)**:
* Ensure the Thunderbolt port on your source computer is functioning correctly. Try connecting other Thunderbolt devices to the port to verify its functionality. If the port is not working, you may need to update drivers or seek hardware repair.
Alternative Solutions: When Target Display Mode Isn’t an Option
If your iMac doesn’t support Target Display Mode, or if you’re having persistent issues, here are some alternative solutions:
* **Use Screen Sharing:** macOS has a built-in screen sharing feature that allows you to access and control one Mac from another. This isn’t quite the same as using the iMac as a dedicated display, but it can be useful for occasional tasks.
* On the target iMac, go to System Preferences > Sharing.
* Enable “Screen Sharing.”
* Note the IP address displayed.
* On the source computer, open Finder and go to Go > Connect to Server.
* Enter `vnc://` followed by the IP address of the target iMac (e.g., `vnc://192.168.1.100`).
* Click “Connect” and enter your username and password for the target iMac.
* **Third-Party Software:** There are third-party software solutions, though their reliability and performance can vary. Research thoroughly before purchasing.
* **Sell the iMac and Buy a Dedicated Monitor:** If all else fails, consider selling your old iMac and using the money to purchase a new external monitor. This ensures you have a reliable and compatible display solution.
Important Considerations Before You Start
* **Back Up Your Data:** Before making any significant changes to your iMac, especially if you’re considering reinstalling macOS, back up your important data using Time Machine or another backup solution.
* **Understand the Limitations:** Target Display Mode is a legacy feature and may not be as seamless or reliable as using a dedicated external monitor. Be prepared for potential troubleshooting and limitations.
* **Check for Updates:** Ensure both your iMac and the source computer have the latest software updates installed. This can resolve compatibility issues and improve performance.
Target Display Mode vs. Sidecar (for Newer iPads)
If you also own a newer iPad, you might be wondering about Apple’s Sidecar feature. Sidecar allows you to use your iPad as a secondary display for your Mac. While Sidecar is a great option, it’s important to note the differences between Target Display Mode and Sidecar:
* **Target Display Mode:** Uses an iMac as a *dedicated* external display. The iMac’s primary function is to display the output from the source computer. The iMac’s own operating system is essentially bypassed when in Target Display Mode.
* **Sidecar:** Extends your Mac’s display to your iPad wirelessly (or via USB). The iPad retains its own functionality and can be used for other tasks while also serving as a secondary display. The iPad is not *dedicated* to being a display. It continues to function as an iPad.
Target Display Mode requires a physical cable connection and is limited to older iMac models. Sidecar is wireless (or wired via USB), supports newer Macs and iPads, and offers more flexibility. Choose the option that best suits your needs and hardware.
Final Thoughts
Using your iMac as an external monitor can be a great way to extend your workspace and repurpose old hardware. By carefully following the steps outlined in this guide and troubleshooting any issues that arise, you can enjoy the benefits of a larger display without the expense of buying a new monitor. Remember to check compatibility, use the correct cables, and be patient during the setup process. With a little effort, you can transform your iMac into a valuable tool for increased productivity.
By following these instructions, you can effectively turn your compatible iMac into a useful external display, saving you money and giving new life to older hardware. Enjoy your extended workspace!