[dba-Tech] Reboot to fix

Does anyone know where the sequence is stored that runs a process when a
Windows computer reboots? 

In a number of situations; for example; replacing a system file, the OS asks
you to reboot before the chances can take place. When the system boots, it
looks at some file/location and uses the information there make the chances.

What and where is this file or location?

TIA
Jim