Windows Service OnStop when computer shutdown

Yes. OnStop() gets called when the machine is shutdown. OnShutdown() is for when you need to know specifically that the machine is being shutdown.

UPDATE: As has been pointed out in the comments since this was first posted, this is no longer necessarily the case. So your code should be written with the assumption that OnStop() may or may not be called when the machine is shut down. If you need to clean up during a shutdown, handle OnShutdown().

Override OnShutdown is the correct method. OnStop is not called during shutdown.

Microsoft Windows has added an option called Fast Startup which does not actually shutdown the computer.

As noted in the Fast Startup setting description, Restart isn't affected. This is why the Restart triggers OnShutdown and Shutdown does not.

Turning off Fast Startup will trigger OnShutdown for both Restart and Shutdown.