Disable Auto-update and Reboot

To turn off automatic updates (and the consequent automatic reboots) on Windows 10

Run the Services applet (services.msc).

Open the Windows Update setting in the list (double click).

Set the Startup type to disabled. Save the settings.

Stop the service.

Note that once this service is disabled, you cannot check for or install updates. The service must be re enabled and restarted in order to do this, after which you will need to follow this procedure again to disable it.

 Supposedly, the service may also become re enabled on its own under some unspecified conditions.

(A supposed alternative method is to set the ethernet connection to be a metered connection, but this does not stop all updates/reboots.)

 To turn off automatic updates (and the consequent automatic reboots) on Windows Server 2016:

Currently it is much easier to configure this than it is on Windows 10.

Run sconfig, choose the Windows Update Settings option. Select Manual.