If you are running Windows 10 on an isolated VM or retro PC with less than 500MB of memory, you may realize that most of the memory is actually used by Defender and Windows Firewall compononents. There is a way to entirely disable these components and prevent them from loading into memory on boot. This is a terrible thing to do, but the following will save you a few hundred megs in RAM usage.
„HKLM\SYSTEM\CurrentControlSet\Services\SecurityHealthService“ Change the parameter for „Start“ from "2“ to "4“.
Careful: This value likes to revert every now and then after feature updates.
Windows 10 Pro: gpedit.msc
Computer Configuration -> Administrative Templates -> Windows Components -> Windows Defender Antivirus [x] Deactivate Windows Defender Antivirus (German: Windows Defender Antivirus deaktivieren)
Windows 10 Home: regedit.exe
HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows Defender New DWORD: DisableAntiSpyware = 1 New DWORD: DisableRoutinelyTakingAction 1
Run Windows Firewall, disable Windows Defender Firewall for all network types
Go to Settings -> System -> Notifications -> Disable Security Notifications