What does the DISKPART command do in Windows XP/2003?

You can use this utility to enable storage configuration from a either a script, a remote session, or another command prompt. DISKPART enhances the Disk Administrator graphical user interface (GUI).
DISKPART enables a superset of the actions that are supported by the Disk Management snap-in. The Disk Management snap-in prohibits you from inadvertently performing actions that may result in data loss. It is recommended that you use the DISKPART utility cautiously because DISKPART enables explicit control of partitions and volumes.

You can use DISKPART to convert a basic disk to a dynamic disk. The basic disk can either be empty or contain either primary partitions or logical drives. The basic disk can be a data disk or system or boot drive. The basic disk cannot have fault-tolerant disk driver (FtDisk) sets such as stripes or mirrors. To convert basic disks that have FtDisk driver sets, use Disk Management on Windows 2000 or convert the disk before you upgrade to Windows XP.
You can use DISKPART to convert a dynamic disk to a basic disk. You must delete any dynamic volumes before the conversion process. It is not recommended that you delete partitions on a dynamic disk except in emergency situations. It is recommended that you delete all volumes on the drive, and then convert the disk to basic. You must delete all dynamic data partitions. Also, never mix the basic primary and dynamic partitions on the same drive. If you do so, the computer may be unable to restart.

You can use DISKPART to create a partition at an explicit disk offset. The Disk Management snap-in places the partition at the end of any occupied area or on the first sufficiently large area. On master boot record (MBR) disks, the partition offset and the size are rounded to preserve the required cylinder alignment. Offsets are rounded to the closest valid value, and the size is always rounded up to the next valid value. DISKPART does not assign a drive letter to a newly created partition. Use the assign command to assign either a mount point or a drive letter.
DISKPART follows the same policy as the snap-in. Dynamic disks can only be created on fixed disks. You cannot convert removable disks, such as 1394 or universal serial bus (USB) drives, to dynamic disks.

Links

A Description of the Diskpart Command-Line Utility – 300415