Primary and Extended Partitions
Typically with DOS, when the hard drive is divided into more than one partition, the first partition is called the primary partition, while the second is called the extended partition. DOS and Windows assign letters to these drives, such as C or D. The primary partition is usually the active partition, that is, the partition that contains boot information.

DOS can have up to four separate primary partitions, or three primary and one extended, two primary and one extended, or just one primary and one extended partition on one hard drive, depending on the user's needs. DOS can have up to four separate partitions on any one hard disk. The extended partition uses the free hard disk space, and is normally assigned all the available space outside the primary partition(s). DOS can only address a maximum of two gigabytes of hard disk space.

Note that only the primary partition on any hard drive can be designated as "active", or bootable. DOS and Windows 95/98 can only manage one primary partition per hard drive. Windows NT, Windows 2000, and some third party disk management utilities do not share this limitation, and can be used to manage multiple primary partitions on a hard drive. A primary partition cannot be subdivided into smaller units.

Logical Drives
When a hard drive is partitioned, including an extended partition, the extended partition uses up all free hard disk space not included in the primary partition(s). There can be only one extended partition per disk, but unlike the primary, it can be subdivided into multiple (up to 23) sections called logical drives. Having multiple logical drives inside the extended partition provides some advantages:

• Information can be rapidly retrieved.
• Multiple operating systems, such as MS DOS and Windows 98, can be installed on the same computer, provided both drives have the same file system or FAT.
• Logical drives physically separate information for organizational and security reasons.

FDISK, Boot Sector, and Partition Table
FDISK is the partitioning program for MS-DOS, Windows 9x (95, 98, and Millennium), UNIX, and Linux. When partitioning a hard drive, the FDISK program creates the disk boot sector. Typically the boot sector is the first area on each logical DOS disk, or partition. When a hard drive is partitioned, the FDISK program creates the disk boot sector. Typically the boot sector is the first area on each logical DOS disk, or partition. When the hard drive is formatted, the information to boot the operating system is recorded in the boot sector. During the partitioning process, FDISK also establishes partition information. On a drive that has been partitioned, the partition information is in the form of a special table, called the partition table. The partition table is located in the boot sector at the very beginning of the disk. Critical information is found in the partition table, including the following:

• The location and starting point of each logical drive on the disk.
• Information on which partition is marked active.
• The location of the master boot record (MBR). Only bootable disks have a master boot record.

The location of the partition table at the beginning of the disk is significant in that this is the point where the system looks for boot up information.