The IOS boot sequence is a process performed after an Cisco IOS device is powered on. The IOS device performs a power-on self-test (POST) to test its hardware components and choose an IOS image to load. The boot sequence consists of the following steps:
1. The device performs the power-on self-test (POST) process to discover and verify its hardware components.
2. If the POST test is successful, the bootstrap program is copied from ROM into RAM.
3. The bootstrap program decides which IOS image to load from the flash memory into RAM, and then loads the chosen IOS.
4. IOS finds the startup configuration file, usually located in NVRAM, and loads it into RAM as the running configuration.