Generally speaking the processor of your PC is yet to begin its processing once you switch it on. When your system memory is empty the processor doesn’t really have anything that it can execute. Actually your processor has no idea where it is.
The manufacturers of BIOS and other chip makers have developed a way in which you can ensure that your PC can boot regardless of the BIOS in the machine. This will allow your processor to start executing its process from the same place every time it is switched on. That place is recorded as FFFF0h.
Every hard disk also has to have a consistent starting point. This is where all the key information is stored regarding the disk. The particulars of this information could include the partitions and their types etc. The BIOS also needs a place where it can load the initial boot program which will start the process known as master boot record. It can be referred to as master boot sector, boot sector or simply MBR.
The exact consistent location of the master boot record is cylinder 0, head 0 and sector 1 which is the first available sector on the disk. This is the place where the BIOS will look when it begins to boot the machine. It will find all the instructions and information regarding the way in which the disk has to be booted and how the operating system should be loaded.
The master boot record consists of three main structures. The first of these is the Master Partition Table. This is a small table that contains all the descriptions regarding the partitions on the hard disk. Only the information that describes four partitions can fit in the master partition table. This is the reason a hard disk is known to have only four true partitions. The partition marked active is the one which is used for booting.
The second most important structure is the Master Boot Code. The initial program that the BIOS has to load and execute in order to start the boot process is contained in the master boot record. The control is eventually transferred to that particular hard disk partition which contains the boot program which has to be used for booting the computer.
Serious data loss can occur if the master boot record is damaged or corrupted in any way. This contains extremely important information and the user will suffer grievous consequences if this information is lost. Most viruses are targeted at the master boot code because this is the first program that is executed when a PC is switched on.
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