The first file loaded is?

Jerry McAllister jerrymc at
Mon Feb 8 16:23:25 UTC 2010

On Mon, Feb 08, 2010 at 09:23:41AM -0500, Decker, Ross wrote:

> I'm just starting my adventure into BSD along with C++.  I know that
> this OS gives you all the source files that are used in the OS. What I'm
> asking, is what is the name of the first file that is loaded and where
> is the source file for it? I want to start with the very first line of
> code and see if I can step my way through the entire boot process. There
> are many things that I see during boot up that I have no idea what they
> are (SMAP Type....) that aren't that Google Friendly.
> So if anyone knows the names of the source files and their locations for
> the boot sequence could you please post them..... SUPER thank you's!

Well, the first thing executed is the BIOS.  
It discovers an MBR to suck in and transfer control to.
The MBR that it chooses is the one on the first one of its
list of boot devices that has an MBR.   That all is pretty much
the same for all PC systems regardless of OS.  Once it loads and
transfers control to the MBR it is dependand on the OS.  The MBR
generally checks a couple things and chooses a boot sector from one
of the bootable partitions to read in and hand over control to.

If you poke around in man pages for boot and init you will learn a lot
of what you are asking.

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