When the power is first applied to the Raspberry Pi, or it has been reset (for more information, see the “Reset” section in Chapter 3 of Raspberry Pi Hardware Reference [Apress, 2014]), a boot sequence is initiated. As you will see in this chapter, it is the GPU that actually brings up the ARM CPU.
The way that the Raspberry Pi is designed, it must be booted from firmware found on the SD card. It cannot boot from any other source. RISC code for the GPU is provided by the Raspberry Pi Foundation in the file bootcode.bin.
After the second-stage boot loader has been executed, it is possible that other operating systems or ARM boot ...