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Major Disk Structures and the Boot Process
File systems organize hard disks and other storage devices so that they can be used. When you are dealing with large storage units in the gigabytes, such as modern hard disk drives, it is necessary to have a structured way of arranging the data. At the highest level, hard disks and other large media must sometimes be broken into multiple pieces for easier use. In any event, it is necessary to have some fundamental structures that make it possible for a PC to determine the characteristics of the file system on the hard disk, to permit the system to be started up and files accessed.
In this section I describe the major disk structures that organize data in the FAT family of file systems (FAT12/FAT16/VFAT/FAT32). I begin by describing the master boot record (MBR) and explaining the way that hard disks are organized into partitions. I also explain what the different partition types are, and what the limitations are in mixing them. I then discuss volume boot sectors and the role of the active partition. Finally, I describe the DOS boot process (which is also used for consumer versions of Windows) and conclude with a discussion of boot sector viruses.
Note: The descriptions in
this section apply to the FAT file systems primarily. If you are using an operating system
like Linux exclusively, then only some of the material in this section will be of
relevance to you. However, all operating systems running on a PC use the high-level
partition structure to some extent, because all file systems on a PC must fit into the
overall partitioning scheme used for PC hardware (though this is a bit of an
Next: Master Boot Record (MBR)