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What Does Happen During Boot Process? - BIOS and MBR

 
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Old 12-11-2009
What Does Happen During Boot Process? - BIOS and MBR
I'm talking about boot process in multi-boot Linux perceptive.

Please tell me whether my explanation is right or wrong? If wrong, please explain.

"The BIOS checks the system and loads this initial bootstrapping code into
memory. This initial bootstrap code searches for an active partition and looks for a first sector of that active partition.

After that, bootstrap code gets whatever boot code (usually GRUB Stage 1) in the VBR and loads it in memory, so GRUB Stage 1 in this case overrides the MBR initial bootstrap that's in memory.

Once GRUB Stage 1 is in memory, it takes GRUB Stage 2 from /boot/ and loads it memory. Thus, GRUB Stage 2 overrides the GRUB Stage 1.

Now once GRUB Stage 2 is in memory, it presents an interface where the user
can select which OS to boot.

Once OS is selected, the GRUB stage 2 loads the selected Kernel into Memory, so the chosen OS Kernel overrides GRUB Stage 2.

Now this Kernel has the control and finishes the process. "

Thanks!
 
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LEARN ABOUT DEBIAN

nvram

NVRAM(4)						   BSD Kernel Interfaces Manual 						  NVRAM(4)

NAME

     nvram -- non-volatile RAM

SYNOPSIS

     To compile this driver into the kernel, place the following line in your kernel configuration file:

	   device nvram

     Alternatively, to load the driver as a module at boot time, place the following line in loader.conf(5):

	   nvram_load="YES"

DESCRIPTION

     The nvram driver provides access to BIOS configuration NVRAM on i386 and amd64 systems.

     PC motherboard uses a small non-volatile memory to store BIOS settings which is usually part of its clock chip and sometimes referred as
     ``CMOS SRAM''.  This driver exposes bytes 14 through 128 of the NVRAM, or a total of 114 bytes, at offset zero of the device file /dev/nvram.

     This driver is useful for cloning machines that shares the same hardware configuration and need same BIOS setting tweaks.

IMPLEMENTATION NOTES

     The BIOS NVRAM's bytes 16 through 31 are checksummed at byte 32.  This driver does not take care for these checksums.

EXAMPLES

     Backup existing BIOS NVRAM to nvram.bin:

	   dd if=/dev/nvram of=nvram.bin

     Restore BIOS NVRAM from nvram.bin:

	   dd if=nvram.bin of=/dev/nvram

SEE ALSO

     dd(1)

HISTORY

     The nvram device driver first appeared in FreeBSD 6.4.

AUTHORS

     The nvram device driver was written by Peter Wemm.  This manual page was written by Xin LI.

BSD
								 February 8, 2010							       BSD