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. This is often called a "true" formatting operation, because it
really creates the physical format that defines where the data is stored on the disk. The
first time that a low-level format ("LLF") is performed on a hard disk, the
disk's platters start out empty. That's the last time the platters will be empty for the
life of the drive. If an LLF is done on a disk with data on it already, the data is
permanently erased (save heroic data recovery measures which are sometimes possible).
If you've explored other areas of this material describing hard disks, you have learned
that modern hard disks are much more precisely designed and built, and much more
complicated than older disks. Older disks had the same number of sectors per track, and
did not use dedicated controllers. It was necessary for the external controller to do the
low-level format, and quite easy to describe the geometry of the
drive to the controller so it could do the LLF. Newer disks use many complex internal
structures, including zoned bit recording to put more sectors
on the outer tracks than the inner ones, and embedded servo
data to control the head actuator. They also transparently map
out bad sectors. Due to this complexity, all modern hard disks are low-level formatted
at the factory for the life of the drive. There's no way for the PC to do an LLF on a
modern IDE/ATA or SCSI hard disk, and there's no reason to try to do so.
Older drives needed to be re-low-level-formatted occasionally because of the thermal
expansion problems associated with using stepper motor
actuators. Over time, the tracks on the platters would move relative to where the
heads expected them to be, and errors would result. These could be corrected by doing a
low-level format, rewriting the tracks in the new positions that the stepper motor moved
the heads to. This is totally unnecessary with modern voice-coil-actuated hard disks.
Warning: You should never
attempt to do a low-level format on an IDE/ATA or SCSI hard disk. Do not try to use
BIOS-based low-level formatting tools on these newer drives. It's unlikely that you will
damage anything if you try to do this (since the drive controller is programmed to ignore
any such LLF attempts), but at best you will be wasting your time. A modern disk can
usually be restored to "like-new" condition by using a zero-fill utility.
Next: High-Level Formatting
