LOW LEVEL FORMATTING-
Low-level formatting is the process of outlining the positions of the tracks and sectors on the hard disk, and writing the control structures that define where the tracks and sectors are. All modern hard disks are low-level formatted at the factory for the life of the drive.
HIGH LEVEL FORMATTING-
High-level formatting is the process of writing the file system structures on the disk that let the disk be used for storing programs and data. High-level formatting is done after the hard disk has been partitioned, even if only one partition is to be used.
The distinction between high-level formatting and low-level formatting is important. It is not necessary to low-level format a disk to erase it: a high-level format will suffice for most purposes; by wiping out the control structures and writing new ones, the old information is lost and the disk appears as new.