System Setup and Software Installation Guide for Cisco ASR 9000 Series Routers, IOS XR Release 6.5.x - Bring-up the Router [Cisco IOS XR Software (End-of-Sale)] - Cisco
CCNA Training » Cisco Router Boot Sequence Tutorial
Cisco 3850 Switch Stuck at Booting - Cisco Community
unable to upgrade ios in cisco switch 3750
CCNA Training » Cisco Router Boot Sequence Tutorial