What is Actually Happening When a Windows Computer is Shutting Down? | Dramel Notes

The system registry is (maybe?) written to the disk. Back when I used Windows XP, I noticed that if you made any changes to the registry then pulled the power, the changes would not be saved. I am not quite sure about this one, just pointing it out.

Here is an excerpt from a document that Microsoft released:

• System session shutdown. This phase includes the pre-shutdown notification and shutdown notification sub-phases.
• Pre-shutdown notification. Windows serially shuts down all services that registered to receive pre-shutdown notifications. Ordered services—services that have set up the shutdown order of dependent services—are shut down before non-ordered services.
• Shutdown notification. All services that registered to receive shutdown notifications are shut down in parallel. If all services have not exited after 20 seconds (in Windows Vista) or 12 seconds (in Windows 7 client operating systems), the system continues the shutdown. Processes and services that do not shut down in a timely manner are left running as the system shuts down.
• Kernel shutdown. The remainder of the system, such as all devices and drivers, are shut down during the kernel shutdown phase.

Basically, what you are waiting on is each individual service to clean up and exit. Each service is given 12 seconds to exit before it is killed.

Half of the shutdown time is dedicated to shutting down system services. If you are really interesting in seeing what time is dedicated to whatever during a shutdown, Windows includes a tool for tracing shutdown time.

• xbootmgr -trace shutdown -numRuns 3 -resultPath %systemdrive% races -postBootDelay 180 -traceFlags base

And to make sense of the generated file (be sure to run in %systemdrive% races)

• xperf -i trace.etl -o summary.xml -a shutdown

Sources

Windows On/Off Transition Performance Analysis Document [Microsoft]

Windows On/Off Transitions Solutions Guide Document [Microsoft]