What happens when the power is turned on
Unlike simple processors where the user's code executes immediately at power on, the AM335x processors feature an internal ROM to offer a variety of choices to start the system. At power on, the internal ROM starts running and looks at the SYSBOOT signals connected to the processor to decide whether to load the user code and to configure the device containing the user code appropriately. The BBB exposes a subset of the available options; this subset can be selected by the user button.
Note that the user button is only checked on power up (not reset!). In the following image, the user button is highlighted. Since the BBW does not have an onboard flash, there is no user button.
Bootloader
Bootloader is the part of the system responsible for loading the operating system. This is similar to the concept of BIOS on desktop systems. By default, if the user button is not depressed, the processor will attempt to boot from the onboard flash on the BBB....
