To use all-in-one PC as monitor for your laptop, you need a direct video connection and the ability to switch the AIO's input source. This setup works best if your all-in-one has an HDMI input port, a DisplayPort, or, for older iMacs, supports Target Display Mode.
Can you use an all-in-one PC as a monitor?
Before you start, confirm that your all-in-one PC has a video input port, typically labeled HDMI IN or DisplayPort. This port is essential for receiving a signal from your laptop. If your AIO lacks these ports, you can still use it as a wireless display with features like Windows "Project to this PC" or third-party applications such as SpaceDesk or Deskreen. This compatibility check saves you time and ensures you have a working path forward.
Connect your laptop to the all-in-one with the right cable
Physically connect your laptop to the all-in-one PC using the appropriate cable. If both devices have HDMI ports, an HDMI cable is all you need. For laptops with USB-C or Thunderbolt ports, use a USB-C to HDMI adapter or a Thunderbolt cable. This direct connection is the foundation for turning your AIO into a dedicated screen.
Switch the all-in-one to the correct input source
After connecting the cable, you typically need to switch the AIO to the correct input source using a dedicated button, often labeled "HDMI IN," "Display Source," or "Input Switch," usually located on the side or bottom of the display. Dell AIOs, such as the OptiPlex 7780 and 7490, have a "Display Built-in Self Test button" on the bottom that also functions to switch between the internal system display and HDMI input when the computer is on. Pressing this button is the critical step that tells the AIO to show your laptop's screen instead of its own.
Use Target Display Mode on a compatible iMac
Apple iMacs support a feature called "Target Display Mode" (TDM) to act as an external display for another Mac. This mode is only available on specific models: 24-inch or 27-inch iMacs from 2009-2010, and any iMac from 2011, 2012, 2013, or mid-2014. For 2009-2010 iMacs, a Mini DisplayPort cable is required for Target Display Mode. For 2011-2014 iMacs, a Thunderbolt or Thunderbolt 2 cable is required. To activate Target Display Mode on a compatible iMac, connect the appropriate cable and press Command-F2 on the iMac's keyboard. If "Use F1, F2, etc. keys as standard function keys" is enabled in Keyboard System Preferences on the iMac, use Command-Fn-F2 instead. Note that iMacs used as a display for TDM must be running macOS High Sierra 10.13.6 or earlier, and the source Mac must be introduced in 2019 or earlier and run macOS Catalina 10.15.8 or earlier. Retina iMacs (Late 2014 onward) and Apple Silicon Macs do not support Target Display Mode due to higher resolution bandwidth requirements and discontinued software support.
Adjust display settings on your laptop
Once the AIO shows your laptop's screen, configure the display settings on your laptop for the best experience. In Windows or macOS, open display settings and set the resolution to match the AIO's native resolution. Choose between Extend or Duplicate modes depending on whether you want a second workspace or a mirror image. This adjustment ensures sharp text and proper scaling across both screens.
Disable the touchscreen and finalize the setup
To prevent accidental input while using the AIO as a monitor, disable its touch functionality. On Windows AIOs, go to Device Manager, find the touchscreen driver under Human Interface Devices, and disable it. On macOS, touch input is not an issue for TDM setups. If your AIO lacks video input ports, wireless alternatives like SpaceDesk can still let you use it as a second screen over your network, but for a wired connection you can often add a second monitor to an all-in-one PC by repurposing its video-in ports. Once connected, you can arrange your workspace with a split screen on laptop and monitor to keep reference material visible while you work. With touch disabled, your all-in-one becomes a clean, dedicated display for your laptop.
