The first thing is POST-Power On Self Test which is nothing but Testing your hardware with CMOS-Complementary Metal Oxide Semiconductor If some Error happens like Floppy does make bothering still your system boot.It ignore similar problems with some beeping. Once your POST is completed Then the RAM is awaked.The instructions tells the hardware to check the boot device which depends on your BIOS configuration.in my system first the hardware checks CD-Rom then it goes to the harddisk. When a boot device is found (assume itis your Harddisk)then your harddisk is told to go to 0th sector(0th head,0th cylinder,0th sector) it is nothing but Master Boot Record(MBR) then load and execute instructions here(MBR).some times MBR also called Master boot block.This block is also used to read the partition table mainly used to find the active partition.Once it finds the active partition, it begins to read and execute the instructions contained within the first block. After Executing the master boot block then it tells which block can execute or not, it may be last sector in last head. you would never know anything was wrong. As for as In linux “boot viruses” are possible which attacks the boot sector it can damage your system..the new viruses can allow CMOS to write into Master boot block it isvery dangerous.Therefore, you need to be especially careful when booting from floppies.mostly it affects when you boot your system using floppy something..so careful ok k if you considered in your windows OS you can see IO.SYS and MSDOS.SYS files.these are real active partition files.you can remove it because it is system files..in Linux point of view LILO(linux Loader) is main file (Partition file) if you ve installed this it is the program you can be executed at first.so you can’t remove this..once again careful..so LILO is a boot loader..
If you want to know deeply inform to me…..cheers…,