- Kernel and
Unlike regular computer, most embedded systems don't have a firmware out-of-box like CMOS, Openfirmware or EFI, etc. Instead, you need to install the bootloader yourself or it is burned onto the board already. Generally, to a naked system, people use JTAG protocol to burn a bootloader. A bootloader can provide a interface for users to control the system as well as basic system tools, such as writing data into flash or transferring files from the host machine.
In computing, the kernel is the central component of most computer operating system; it is a bridge between applications and the actual data processing done at the hardware level. The kernel's responsibilities include managing the system's resources (the communication between hardware and software components). Usually as a basic component of an operating system, a kernel can provide the lowest-level abstraction layer for the resources (especially processors and I/O devices) that application software must control to perform its function. It typically makes these facilities available to application processes through inter-process communication mechanisms and system calls.
The Linux kernel is an operating system kernel used by the Linux family of Unix-Like Operating system. It is one of the most prominent examples of free and open source software.
The Root Filesystem :
Other than the Linux kernel, most embedded Linux system contain things such as a graphic environment as on most PDAs. The collection of all those files is called the Root Filesystem. It generally is stored in the flash partition called root. Attention, here "Root" is not equal to the /root directory and here "filesystem" is not a software to manager files on storage devices. The Root Filesystem is in the form of an image to be written into the flash memory.