Low-level formatting and High-level formatting

Low-Level Formatting

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 sector. 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.

Utility for Low-Level Format

HDD Low Level Format Tool is a freeware utility for low-level hard disk drive formatting.

• Supported interfaces: S-ATA (SATA), IDE (E-IDE), SCSI, USB, FIREWIRE. Big drives (LBA-48) are supported.
  
• Supported Manufacturers: Maxtor, Hitachi, Seagate, Samsung, Toshiba, Fujitsu, IBM, Quantum, Western Digital.
  
• The program also supports low-level formatting of FLASH cards using a card-reader.

This freeware Low Level Format utility will erase, Low-Level Format and re-certify a SATA, IDE or SCSI hard disk drive with any size of up to 281 474 976 710 655 bytes. Will work with USB and FIREWIRE external drive enclosures. Low-level formatting of Flash Cards is supported too. Low Level Format Tool will clear partitions, MBR, and every bit of user data. The data cannot be recovered after using this utility. The program utilizes Ultra-DMA transfers when possible.

WARNING: After running this free low level format tool, the whole disk surface will be fully erased.
Therefore, data restoration will be impossible after using this utility! Use

Operating System: MS Windows 2000SP4/2003/XP

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High-Level Formatting

After low-level formatting is complete, we have a disk with tracks and sectors--but nothing written on them. High-level formatting is the process of writing the file system structures on the disk that let the disk be used for storing programs and data. If you are using DOS, for example, the DOS FORMAT command performs this work, writing such structures as the master boot record and file allocation tables to the disk. High-level formatting is done after the hard disk has been partitioned, even if only one partition is to be used. See here for a full description of DOS structures, also used for Windows 3.x and Windows 9x systems.

The distinction between high-level formatting and low-level formatting is important. It is not necessary to low-level format a disk to erase it: a high-level format will suffice for most purposes; by wiping out the control structures and writing new ones, the old information is lost and the disk appears as new. (Much of the old data is still on the disk, but the access paths to it have been wiped out.) Under some circumstances a high-level format won't fix problems with the hard disk and a zero-fill utility may be necessary.

Different operating systems use different high-level format programs, because they use different file systems. However, the low-level format, which is the real place where tracks and sectors are recorded, is the same.