Before the device is powered on, the device CPU will be in a state where no initializations have been done. Once the Android device is powered on, execution starts with the boot ROM code. This boot ROM code is specific to the CPU the device is using. As demonstrated in the following screenshot, this phase includes two steps, A and B:

• Step A: When the boot ROM code is executed, it initializes the device hardware and tries to detect the boot media. Hence, the boot ROM code scans until it finds the boot media. This is almost similar to the BIOS function in the boot process of a computer.
• Step B: Once the boot sequence is established, the initial boot loader is copied to the internal RAM. After this, the execution shifts to the code loaded into RAM: