IBoot (Bootloader)

This is Apple's bootloader for the S5L8900. It runs what is known as Recovery Mode. It has an interactive interface which can be used over USB or serial.

In versions pre 2.0, there was an exploit in the diags command.

There is a modified iBoot : OpeniBoot, a free and Open Source replacement of iBoot. Its goals is to have low-level drivers in order to load linux on the iPhone.