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.
More input from FAQ Farmers:
Low level formatting is a hard disk operation that should make recovering data from your storage devices.
A low-level format is the process that marks the location of tracks and sectors on a disk. A disk cannot be partitioned or formatted until a low-level format is completed.
"low-level" is imprecise here; all formatting is "low-level" anyway... That said, steer clear of utilities that specifically talk about 'low level' formats and were not made by your drive manufacturer, some of them can easily do damage to a drive for which they were not intended and which they do not properly understand.
A low-level partition is a disk partition that has been low-level formatted. This means formatting in such a way that the data once stored in the partition is completely irrecoverable.
That would be called low-level formatting.
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Low-level formatting
racks and sectors
A low level language is one where there are only a few (or even only one) instruction(s) per line of code. Assembler is an example of a low level language.
high-level formatting
You can do a low level format ... this will not destroy all your files. To perform a complete formatting, you will need a system diskette or CD for that particular drive.
Low-Level formatting is used to outline areas (tracks and sectors) on the hard drive so physically the hard drive is ready to be used. So low level formatting is so called "PHYSICAL Formatting" which means all of your old data are physically wiped out and create a new structure on your disk. So when you add new data, it just add into your empty disk. High level formatting is so called "LOGICAL Formatting" which means that all the old data in your disk will not be completely erased (they are still in your disk) but the access path to those data has been wiped out. So you cannot access those data anymore (e.g. access path is like your address book. when you lost the address book, you won't know where your friends stay and can't contact them (same analogy)) However, your disk will show as empty. Okay, again when you want to store new data in your disk, it will create new access path and replace old data with your newly stored data. This formatting changes the file system on the hard drive so the Operating System that you use can write and save data to the hard drive.:)