Use iMac as an External Display (Extended Display) for MacBook Pro

Using iMac as an External Display for MacBook Pro (Extended Display)

Reference Documents

First, be sure to check Apple's official documentation:

• Use an iMac as a display with Target Display Mode

• Using a 2013 21-inch iMac as an external display for a 2016 MacBook Pro

Lulian's website also provides detailed guides:

• How to Use an Apple iMac as a Display, as an Extended Screen for MacBook

Device Requirements

To use an iMac as an extended display for a MacBook, the devices must meet the following conditions (based on information obtained from Apple support):

• The iMac must be an older model, and its macOS version must be 10.13.6 or lower.

• The MacBook must be a 2019 model or older, and its macOS version must be 10.15 or lower.

My MacBook Pro is a 2016 model (with Touch Bar), and all its ports are USB-C. See below:

My iMac is a 2013 model with Thunderbolt 2 ports. See below:

Adapter Cables

To connect the iMac to the MacBook Pro, you need to purchase adapter cables. It is recommended to use official Apple adapters:

• Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter | 384 CNY

• Thunderbolt 2 Cable (2.0 m) | 285 CNY

Note: Thunderbolt 2 and Mini DisplayPort are different, although their physical connectors look identical. Thunderbolt 2 is more advanced than Mini DisplayPort. You can choose either one.

Step-by-Step Instructions

After purchasing the adapter cables, follow the official guide here. The steps are as follows:

To begin using your iMac as a display:

1. Make sure your iMac is powered on and the other Mac is logged into a macOS user account.

2. Connect the Mini DisplayPort or Thunderbolt cable between the two computers.

3. Press Command + F2 on the keyboard of the iMac that will serve as the display.

Important: Pressing Command + F2 is essential for the iMac to function as an extended desktop for the MacBook Pro. This step must be performed; otherwise, it will not work.

Issue with External Keyboard on iMac

My iMac uses an official Apple wireless Bluetooth keyboard. Pressing Command + F2 works fine with this keyboard.

However, with regular external keyboards, pressing Command + F2 does not work. Here are two solutions:

Method 1: Press fn + Command + F2 on a standard keyboard. I haven’t tested this, as it requires a keyboard with a dedicated fn key.

Method 2: Install the software KeyRemap4MacBook and remap the F2 key to display_brightness_increment. Example configuration:

Method 2 has been tested and works. I discovered this solution from the article Trying iMac TDM Mode. It also introduced me to the term TDM (Target Display Mode), which refers to the mode in which an iMac functions as an external display.

Additionally, here’s an interesting related article: Can a Third-Party Keyboard Activate iMac TDM? Not a Chance!

(Note: Both links above are now broken.)