raspberry pi sd card layout

Partition	Type	Size	Contents
1	FAT	220 MB	start.elf, bootcode.bin, fixup.dat, start.elf, LICENCE.broadcom, LICENSE.oracle: copied from https://github.com/raspberrypi/firmware kernel.img: U-boot boot.scr: U-boot start up script recovery_frimware: recovery firmware (<= 20MB) frimware_selected: text file determine which firmware will be loaded frimware_0: firmware #0 (<=100MB) frimware_1: firmware #1 (<=100MB)
2	Ext4	Remaining of SD card	Config data

if U-boot cannot start the normal boot proccess, it will load the recovery_frimware to let user recovery the system