Hardware Reference
In-Depth Information
available.Ofcourse,youshouldbackupanyexistingdataonanydrivebeforeperforming
partition alignment or creation.
Disk Formatting
There are two types of disk formats:
• Physical, or low-level formatting
• Logical, or high-level formatting
When a blank floppy disk is formatted, Windows Explorer or the
FORMAT
command per-
formsbothtypesofformatssimultaneously.Ifthefloppywasalreadyformatted,DOSand
Windows will default to doing only a high-level format.
The
FORMAT
command works differently on a hard disk performing only the high-level
format. The low-level formatting is done at the factory on all modern drives. In addition,
partitioning is required before a volume can be high-level formatted, because a hard disk
is designed to be used with more than one OS or file system and may have more than one
partition orvolume.Usingmultiple operatingorfilesystemsononeharddriveispossible
by partitioning, which creates multiple volumes on the drive. A
volume
or
logical drive
is
any section of the disk to which the OS assigns a drive letter or name.
Consequently, preparing an HDD for data storage involves three steps:
2.
Partitioning
Low-Level Formatting
During a low-level format, the tracks are divided into a specific number of sectors, creat-
ing the intersector and intertrack gaps and recording the sector header and trailer informa-
tion. The sector's data areas are filled with a dummy byte value ora pattern oftest values.
For floppy disks, the number of sectors recorded on each track depends on the type of
diskette and drive. For hard disks, the number of sectors per track depends on the drive
and the controller interface.
The original ST-506/412 MFM controllers always placed 17 sectors per track on a disk,
ST-506/412 controllers with RLL encoding increased the number of sectors to 25 or 26
per track, and ESDI drives had 32 or more sectors per track. The ATA drives found in
PCstodaycanhaveanywherefrom17to2,500ormorephysicalsectorspertrack,andthe
number of sectors can vary among different tracks.
