These days formatting your hard drive is generally a necessary task only if it’s new to a particular system and even then this will typically be a high level format. High level formatting does not erase all the data on the disk. Rather, it prepares a disk for reading and writing by erasing “bookkeeping” information on the disk, does some simple testing to make sure all sectors are reliable and then creates internal address tables that it later uses to locate new information. I have run into situations when it becomes necessary to perform a low level format on a hard drive as a last ditch effort to resurrect it when no other solutions work, but this has become increasingly rare in recent years. Because low level formatting erases a disk entirely it will effectively get rid of any software, drivers, sector address table and all other data leaving your hard drive like new and ready to start fresh. It also takes a lot longer to do, largely because the drive has to go through and initialize every sector individually. With either type of format your data is effectively erased so be sure to back it up first. However, when committing to a low level format everything really does get erased. Even specialized programs can no longer find in on the drive because it’s truly gone…forever.