Merge pull request SamyPesse#56 from mandliya/patch-1

Magic Bytes Explanation

Chapter-3/README.md

@@ -8,7 +8,7 @@ The BIOS boot sequence is: RAM detection -> Hardware detection/Initialization ->
 
 The most important step for us is the "Boot sequence", where the BIOS is done with its initialization and tries to transfer control to the next stage of the bootloader process.
 
-During the "Boot sequence", the BIOS will try to determine a "boot device" (e.g. floppy disk, hard-disk, CD, USB flash memory device or network). Our Operating System will initially boot from the hard-disk (but it will be possible to boot it from a CD or a USB flash memory device in future). A device is considered bootable if the bootsector contains the valid signature bytes `0x55` and `0xAA` at offsets 511 and 512 respectively.
+During the "Boot sequence", the BIOS will try to determine a "boot device" (e.g. floppy disk, hard-disk, CD, USB flash memory device or network). Our Operating System will initially boot from the hard-disk (but it will be possible to boot it from a CD or a USB flash memory device in future). A device is considered bootable if the bootsector contains the valid signature bytes `0x55` and `0xAA` at offsets 511 and 512 respectively (called the magic bytes of Master Boot Record (MBR), This signature is represented (in binary) as 0b1010101001010101. The alternating bit pattern was thought to be a protection against certain failures (drive or controller). If this pattern is garbled or 0x00, the device is not considered bootable)
 
 BIOS physically searches for a boot device by loading the first 512 bytes from the bootsector of each device into physical memory, starting at the address `0x7C00` (1 KiB below the 32 KiB mark). When the valid signature bytes are detected, BIOS transfers control to the `0x7C00` memory address (via a jump instruction) in order to execute the bootsector code.