Windows Defender runs mostly in the background. It will scan new files for threats, and it will also examine any file that you download via the browser, regardless if you’re using Edge or Chrome, or some other browser. It never really runs full system scans while you’re actively using your PC. It will run a scan when it knows you’re away. That said, if you’d like to limit Windows Defender CPU usage so that it never uses the CPU too much, you can.
Microsoft has a documented method that lets you limit Windows Defender CPU usage. It only requires a little command to be run in PowerShell however, you will need admin rights to run it.
Limit Windows Defender CPU usage
The CPU usage is set as a percentage of your CPU’s total processing power. By default, Windows Defender can use up to 50% of the CPU. Decide how much CPU you want Windows Defender to be able to use.
Open PowerShell with admin rights. Run the following command but replace the number at the end with how much CPU usage you want to allocate to Windows Defender.
Set-MpPreference -ScanAvgCPULoadFactor 50
You can increase the limit beyond 50% if you like but you cannot reduce it to 0. All that does is disable throttling which means Windows Defender will use as much of your CPU as it wants.
The throttling applies to when Windows Defender runs a full scan and will be applied when it tends to start running if your system is idle. This may have an impact on how much time it takes to run a full scan on your system. It won’t impact how well Windows Defender can protect your system and it certainly won’t turn off the scans it runs when you download new files to your system. If you often think about disabling Windows Defender simply because it slows you system down too much, this is a far better alternative.
As for why you should limit CPU usage for Windows Defender, the app tends to drag everything down. If you happen to have an HDD instead of an SSD, you will notice that your system slows down much too much when Windows Defender runs its scans. If your system has an SSD though, chances are you won’t notice Windows Defender running all that much. They may be expensive but SSDs make a huge difference.
Change the throttling level around until you have something that doesn’t slow your system down too much but also manages to run at least one scan a week.
Source = “https://www.addictivetips.com/windows-tips/limit-windows-defender-cpu-usage-windows-10/”