How to check performance with an external display

Your laptop feels slower after you connect an external monitor, or you want to know whether the extra screen changes processor performance. A quick comparison can help separate a real CPU slowdown from changes in graphics, power, or temperature.

Use the Processor Test to compare scores with the display disconnected and connected. Keep the test conditions as similar as possible, because power mode, background apps, and heat can change the result too.

Compare performance with the display connected

Open the Processor Test with your external display disconnected. Keep the laptop plugged in or unplugged for the whole comparison, and close demanding apps.
Run the test and note both the single-core and all-core scores. These scores are out of 100. Write down which display and power settings you are using as well.
Wait a few minutes if the computer feels hot, then connect the external display. Use the same browser, keep the same tabs open, and avoid changing power settings.
Run the Processor Test again and record both scores. If you want a more reliable comparison, repeat each setup two more times and compare the typical scores, not just the highest one.
Disconnect the monitor and run the test once more if the connected result was much lower. This helps show whether the change follows the display connection or was a temporary fluctuation.

Do not run repeated tests if the laptop becomes unusually hot. Let it cool before continuing. A processor test creates work for the CPU, and heat can lower performance during later runs.

What the result means

The scores are close in both setups

A small difference is normal. Browser tests can vary slightly from one run to another as other computer tasks start and stop. If the scores are broadly similar, the external display probably is not reducing your processor performance in a meaningful way.

The scores drop only with the external display connected

Repeat the comparison once under the same conditions. If both scores are consistently lower, check whether connecting the monitor also changed the laptop's power mode, temperature, or background workload. A display connection can add some work for the computer, but a large processor score drop is not proof that the monitor is faulty.

The all-core score drops more than the single-core score

The all-core test keeps more of the processor busy, so it is more likely to expose heat or power limits. If the laptop was warmer during that run, its cooling system may have reduced CPU speed. Let it cool and compare again before drawing a conclusion.

The scores match, but the computer still feels less responsive

The processor score does not measure every part of display performance. A higher resolution, a faster refresh rate, or an application drawing across two screens can put extra work on graphics and the browser's display system. You may notice that as stutter or lag even when the CPU scores remain similar.

How to investigate a lower score

Use the same power state. Keep the computer plugged in or unplugged for both tests. On Windows 11, check Settings › System › Power & battery and keep Power mode the same. On a Mac laptop, check System Settings › Battery and keep Low Power Mode in the same state.
Close busy apps and tabs. Video calls, large downloads, game launchers, and browser tabs with moving content can use processor time. Close them before each run, and wait for updates or file copying to finish.
Check for heat. Put the laptop on a hard, flat surface and make sure its vents are not blocked. If the connected-display run follows a longer period of work, allow the computer to cool and rerun the comparison.
Match the display setup. On Windows 11, open Settings › System › Display to review resolution and layout. On macOS, open System Settings › Displays. Keep the external monitor's resolution and refresh rate unchanged during repeat comparisons.
Test without other display changes. Connect the monitor directly if possible, rather than changing docks or adapters between runs. If you use a dock, keep the same dock, cable, and port for each comparison.
Restart and repeat if results remain inconsistent. A restart clears stuck background tasks. After restarting, use the same browser and test setup, then compare the results again.

Why an external display can affect how fast the computer feels

The processor test measures CPU performance in the browser, not the whole graphics pipeline. The processor handles general calculations, while the graphics processor and display system handle much of the work needed to draw and refresh images on screen.

An external display may use a different resolution or refresh rate from the laptop's built-in screen. That can change graphics workload, but it does not necessarily make the CPU slower. If the CPU scores stay close while animations or scrolling become choppy, the issue may be related to graphics, display settings, or the connection rather than processor speed.

The Processor Test runs in your browser, so treat its scores as a comparison between your own test setups, not as a diagnosis of every part of the computer.