Firmware is a kind of software that is written to a hardware device in order to control user applications and various system functions. The firmware contains low level programming code that enables software to access hardware functions. Devices that run firmware are known as embedded systems which have limited hardware resources, such as storage capabilities as well as memory. Examples of embedded devices that run firmware are smartphones, traffic lights, connected vehicles, some types of computers, drones, and cable set-top boxes.

It is apparent that embedded technology and the firmware that runs on these devices controls our daily lives, from the critical infrastructure cities rely on, to bank ATMs and the homes that consumers live in. It is important to understand what a firmware binary consists of as well as its associated properties. Firmware is comprised of a bootloader, kernel, filesystem, and various other resources. There are different types of firmware built upon embedded Linux, embedded Windows, Windows IoT core, and various Real Time Operating Systems (RTOS). This book will be geared toward an embedded Linux environment, however, the principles will remain platform agnostic.

The following diagram represents what a piece of firmware contains: flash contents, the bootloader, the kernel, and a root filesystem: