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Appendix A. Partitions and file systems
A.1
Hard disk partitions
The mechanism that allows you to install several operating systems on a single PC
or to carve up a single physical disk drive into multiple "logical" disk drives is called
partitioning.
Partitioning is performed by special applications. In MS-DOS and Windows, these
are FDISK and Disk Administrator.
Partitioning programs perform the following:
• create a primary partition
• create an extended partition that can be split into several logical disks
• set an active partition (applied to a single primary partition only)
Information about partitions on a hard disk is stored in a special disk area – in the 1
of cylinder 0, header 0, which is called the partition table. This sector is called the master
boot record, or MBR.
A physical hard disk might contain up to four partitions. This limit is forced by the partition
table that is suitable for four strings only. However, this does not mean you can have only
four operating systems on your PC! Applications called disk managers support far more
operating systems on disks. For example, Acronis OS Selector, a component of Acronis Disk
Director Suite, enables you to install up to 100 operating systems!
A.2
File systems
An operating system gives the user the ability to work with data by supporting some
type of file system on a partition.
All file systems are made of structures that are necessary to store and manage
data. These structures are usually composed of operating system boot sectors,
folders and files. File systems perform the following basic functions:
• track occupied and free disk space (and bad sectors, if any)
• support folders and file names
• track physical location of files on disks
Different operating systems use different file systems. Some operating systems are
able to work with only one file system while others can use several of them. Here
are some of the most widely used file systems:
A.2.1
FAT16
The FAT16 file system is widely used by DOS (DR-DOS, MS-DOS, PC-DOS, PTS-DOS
and other), Windows 98/Me, and Windows NT/2000/XP operating systems and is
supported by most other systems.
Main features of FAT16 are the file allocation table (FAT) and clusters. FAT is the
core of the file system. To increase data safety, it is possible to have several copies
of the FAT (there are usually two of them) on a single disk. A cluster is a minimum
data storage unit in FAT16 file system. One cluster contains a fixed number of
sectors. FAT stores information about what clusters are free, what clusters are bad,
and also defines in which clusters files are stored.
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