A partition on a hard disk device is a unique segment that is separate from other segments on the device.
A typical hard disk is a physical disk or a USB device that contains primary partitions, extended partitions, or logical drives. A partition or a logical drive can also be called a volume.
A primary partition (also called a boot partition) contains one file system. In most versions of Microsoft Windows operating systems, the first partition (drive C:) must be a "primary partition".
A common partition type code for a primary partition used with Microsoft Windows NT 4.x, Windows 2000 and Windows XP is NTFS.
The number of partitions you can create on a hard disk or a USB device depends on the device's partition style. In Windows, the MBR (Master Boot Record) describes how a disk is partitioned, which partition contains the boot sector and where the boot sector is located.
On MBR devices, you can create up to four primary partitions, or you can create up to three primary partitions and one extended partition. You may create only one extended partition on a drive device. Within the extended partition, you can create an unlimited number of logical drives.
You can add more space to an existing primary partition by extending it into adjacent, contiguous unallocated space on the same disk. To extend a partition, it must be formatted with the NTFS file system. You can extend a logical drive within contiguous free space in the extended partition that contains it.
If you extend a logical drive beyond the free space available in the extended partition, the extended partition grows to contain the logical drive as long as the extended partition is followed by contiguous unallocated space.