After the completion of Boot loader program, Which is the kernel code that may be executed(Architecture Dependent assembly/C code)?
I simply meant the very first code of kernel in which directory?

Shall I get some links to PDF/Books for tracing the kernel sequences?

The initial startup sequences are always architecture-specific.

For instance, in the x86 architecture, the first part is probably /usr/src/linux/arch/x86/boot/main.c. (At least, for the primary CPU...)

This very-first stage of the boot process (on the x86...) finds itself in "real mode." That is to say, virtual-memory and other fundamental capabilities do not yet exist. So, the very first job is to set up the processor data-structures necessary to enter the so-called "protected mode." From there, remaining data structures are set-up to allow the kernel to avail itself of other fundamental capacities, such as memory-management, multi-CPU handling, and processes.

Each CPU-type upon which Linux has been implemented ... from the smallest handheld device to the biggest "big iron" mainframe ... has its own specific version of this startup sequence.

Thank You,

I think the defferent architecture and board have its own code
and no common code at very first.

Thank You.

Related with this issue I have a question which I am wondering
about for a long time.

While loading the kernel the processor is still in real mode.
However in real mode it can only address about 1MB + upper memory.
Usually a Kernel is much bigger than that amount.

How does it works?

Hi,
When it starts to load the kernel switches to protected mode.
It does it very early on.
Here is how it works.
http://www.xs4all.nl/~lennartb/bootloaders/node3.html

cheers

thanks nigelc, its a real interesting page. However
I did not get the point yet. Must the kernel be small
enough before decompressing to fit in to the available
memory in real mode?

It is my distinct impression that the compressed image must fit there, but the uncompressed image does not. It will be relocated into protected-mode memory.

There are various curiosities about the initial-stage of the boot process on the x86 processors, which after all was designed with floppy disks in mind. The black actually-floppy ones with a big slot.