A+: Managing Disk Partitions
Hard drives (whether PATA, SATA or SCSI) and drive-like drvices (such as USB Flash Memory Drives) must be partitioned before use (although the latter are preformatted before packaging). Repartitioning destroys any data on the drive so BE CAREFUL.
A partition determines if a drive can boot a PC, how many drive letters the hard disk can have, and whether space is set aside for future or other use.
Once the partition is created, it defines a drive letter for the logical drive. Phyisical and logical drives must then be formatted to build the file system before they can hold data.
Only a primary partition can be bootable and it can only have one drive letter. Only one primary partition can be active in a Windows PC. If you have a simple system, that's all you need, and most systems are set up this way.
Extended partitions can't boot and don't have drive letters themselves, but you can create one or more logical drives which then can be formatted. These partitions can hold data, including image files used to recover a PC to its original state.