reboot.exe is a dos based application used to REBOOT the computer. Users are allowed to set delays for REBOOTs through the command line prompter.
Non-system processes like reboot.exe originate from software you installed on your system. Since most applications store data in your system's registry, it is likely that your registry has suffered fragmentation and accumulated invalid entries which can affect your PC's performance. It is recommended that you check your registry to identify slowdown issues.