Before restoring data, hard disk usually needs low-level format, partition, high-level format to be used. The function is establishing certain data logical structure on physical hard disk. Usually hard disk is divided into 5 regions: MBR, DBR, DIR, FAT and DATA (Here we do not introduce FAT and NTFS file system), which altogether store and manage data.

Low level format
After setting parameter of hard disk in CMOS Setting, why the hard disk is still unusable? That’s about Cylinder, Header and Sector. When hard disk is firstly made in the factory, it usually is “blank”. Only after partitioning tracks and sectors, we can save data on hard disk (Now, before leaving the factory, many disks have been low-level formatted. So you may need not do the
operation, but it is not unnecessary.)

Main functions of low level format
Low level format can also be called physical format, whose functions are to detect the magnetic media, to partition tracks, to partition sectors for each track,  and to arrange the order of partitions in track according to the interleave the customer choose. Its main functions are as following:

1. Test the hard disk media
2. Partition tracks for hard disk
3. Arrange sectors for each track according to the specified interleave
4. Set the sector ID to each track and finish setting sectors
5. Test the hard disk surface, mark “bad” to the damaged track and sector
6. Write a certain ASCⅡ to each sector of hard disk

Hard disk is an important storage resource in computer system. Do not low-level format the hard disk unless it is the only thing possible. For hard disk being used, you need back up important data before low level format; even if back up is unnecessary, it may take much time to partition, high-level format, and install system and application programs. Usually, low level format can be used in the following cases:

When you have bought a new hard disk or hard disk adapter, you’d better low level format it again, which is for the better matching of hard disk and hard disk adapter.

“Bad” sectors, which result from long-time operation, often cause “sector not found” error in DOS. This is because of the loss of sector ID. Sector ID is used to distinguish the sectors. It is marked onto disk as the magnetization map, which however, may dribble away for long-time storage or use. Low level format is the only way for computer users to refresh sector ID in disk. This assignment cannot be done by high level format.

Appropriate set of interleave can fasten data transfer. In most conditions, low level format is the only way to change the interleave.

When there are always inexplicable problems, you can take low level format into consideration.

Ways to low-level format
There are many ways to low-level format. In early time, it can be completed in CMOS or by some special disk tools, or by writing some short programs in Debug. Nowadays, people usually use special tools provided free by hard disk manufacturers.

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