As touched on previously, Windows XP supports two types of hard disk storage: basic disks and dynamic disks. Dynamic storage is newer, and it offers a much greater level of flexibility for dividing up your hard disk real estate.
As you saw, basic disks use partition-based storage. This storage type is a holdover from previous Windows versions, and it is kept around in part for purposes of backward compatibility. In other words, if you took a basic disk full of mp3s from your XP machine and slapped it into a Windows Me system, the Me computer would be able to play the music. If your XP disk were a dynamic disk, however, this would not be the case.
Two types of partitions are available on a basic disk: primary partitions and extendedpartitions.
The first partition on a hard drive is always a primary partition. The law about primary partitions is that all space in the primary partition is assigned a single logical drive letter. Before the primary partition can store files, then, it is formatted with only one file system. You can mix and match file systems on a hard drive, but you can't mix and match them on a single logical drive.
As mentioned earlier, you can configure up to four primary partitions on a single disk. This limits you to four drive letters per drive when using basic storage. Or does it? To circumvent this drive letter restriction, you can use an extended partition.
After creating a primary partition, you can set up an extended partition. Unlike primary partitions, the space in an extended partition can be further subdivided. Each slice in the extended partition is assigned a drive letter.
When using an extended partition, you reduce the number of primary partitions available by one, so that now you can have up to three primary partitions and one extended partition. An extended partition lets you come up with logical drive configurations like the one you see in Figure 4-8.
Figure 4-8. Using an extended partition to create multiple logical drives.
You cannot have more that one extended partition on a single disk. Also, the extended partition can't be the system partition because extended partitions can't be marked as active. The active partition is designated as the system partition, and generally, you'll never need to change what XP recognizes as the active partition.
However, a logical drive on an extended partition can serve as the boot partitionit can hold the operating system's installation directory. For example, it's possible for a Windows XP computer to boot to a system partition formatted with FAT and then run off an extended boot partition that is formatted with NTFS.
Partitioning's big drawback is that once the partitions are created, they are set in stone. Even if the hard drive has lots of unused room, there's no way to add more space to the existing partition without re-creating the entire thing. Of course, this means that all data on the partition is lost, and you have to restore it from backup.
To avoid these restrictions, consider upgrading your disks to dynamic storage.