External HDMI Monitor Significantly Slows Down MacBook Pro

Imagine a situation when the external HDMI monitor suddenly slows down your Mac to unbearable speeds. Not many MacBook Pro owners face this problem, and it is not a good indicator. The monitor may show the image properly while the machine turns totally unusable. It means a user cannot watch videos and the computer may stop working at all. Most Mac owners get really mad as they invest a lot of money in their Apple computers. Thus, they wonder why it is impossible to output a smooth HDMI signal without crushing the machine.

The bad news is that no Mac should demonstrate a drop in working speed because of the external display. There is something wrong, and the problem is not common.

The Potential Causes of the Problem

It is important to tell which applications are running at that time and the amount of RAM available. Harmful apps and lack of free space are two primary reasons for such misbehavior.

The typical scenario is when a user plugs the device into the external display using HDMI adapter. A device then starts acting as it dies. For instance, its productivity and speed may decrease by roughly 20%. That is why it becomes impossible to launch movie files. It is a frustrating situation, but there are several things a user may do.

Ways to Monitor the Health of Your Mac

The next question a user may have is whether it is worth bringing the device to the official Apple Store searching for help. Not everyone needs external monitors, but if you are a producer, designer, or animator, it is hard to imagine another way out. Thus, it is better to fix the issue.

Start by checking the memory usage. You can do that with the help of a built-in utility called Activity Monitor. It is impossible to define the cause of slowdown without analyzing the overall performance. The Activity Monitor window has all necessary details.

  1. Launch Utilities from the Launchpad tool. Launch Activity Monitor.
  2. Pick System Memory at the bottom.

Explore the information carefully to detect the problem. The tool will let you known which processes require most of the system resources as well as whether your Mac has enough space.

Pay attention to the system memory usage in the Dock. Observe a graph of the memory usage in the Dock icon.

  • Launch Activity
  • Select ViewàDock IconàShow Memory Usage. You may modify the color of items in the graph based on your preferences.

To change the colors in the system memory usage graph, do the following:

  • Launch Activity Monitor.
  • Pick System Memory at the bottom.
  • Click the color box near every item and choose the desired color.

Try to check HDMI adapter before/after Activity Monitor results show up. Pay attention to the CPU tab. You may notice that after plugging in the adapter and hooking up the monitor, the situation becomes worse. The problem is obvious: Something leads CPU to becoming fully inefficient. It takes roughly ten to thirty seconds for the process to happen. Firstly, the CPU stays at the low level, but when the content achieves another screen, each core appears to be occupied by about 80%!

Recommended Solution: Resetting PRAM/NVRAM

Before hurrying up to the nearest Apple Store, try resetting the PRAM/NVRAM. It is an effective troubleshooting strategy, which helps to fix many bugs.

  1. Turn off the Apple computer.
  2. Switch your device on and push the Option, Command, P, and R keys at a time. Let them go in approximately 20 seconds. The computer should reboot.


  • On Macs that make a startup sound, let the keys go once you hear the second boot up sound.
  • As for iMac Pro, release the key combination once the company’s logo shows up and goes away for the second time.

3. After the bootup process is complete, launch System Preferences and adjust the reset settings (e.g., volume, screen resolution, boot up disk choice, or time zone).

Important notice: Make sure a firmware password is disabled.

One more thing to remember is that runaway software can shorten the battery runtime. That is what may be causing the problem too. It is better to detect and uninstall such applications.

If nothing helps, turn to the Apple Store for the appropriate actions.