In summary, for a proper LLF, the drive should be

•  At a normal operating temperature

•  In a normal operating position

•  Mounted in the host system (if the drive HDA is not shock-mounted or isolated from the drive frame by rubber bushings)

Low-Level Format

Of these procedures, the LLF is most important to ensure trouble-free operation of the drive. This format is the most critical of the operations and must be done correctly for the drive to work properly. The LLF includes several subprocedures:

•  Scanning for existing defect mapping

•  Selecting the interleave

•  Formatting and marking (or remarking) manufacturer defects

•  Running a surface analysis

On all new systems, these subprocedures are performed automatically by the system's LLF program and require no user intervention, and you need not continue in this section. On older systems, you must take the initiative and should read the section on low level formatting included in the complete text of Upgrading and Repairing PCs, Eighth Edition.

All new drives are low-level formatted by the manufacturer. If you bought a system with a drive already installed by the manufacturer or dealer, an LLF probably was done for you. Most manufacturers no longer recommend you LLF any IDE type drive.

Why Low-Level Format?

Even though it generally is not necessary (or even recommended) to LLF IDE or SCSI drives, there are a few good reasons to consider an LLF. One reason is that an LLF will wipe out all the data on a drive, ensuring that other people will not be able to read or recover that data. This procedure is useful if you are selling a system and do not want your data to be readable by the purchaser. Another reason for wiping all the data from a drive is to remove corrupted or non-DOS operating-system partitions and even virus infections. The best reason is for defect management. As you may have noticed, most ATA-IDE drives appear to have no "bytes in bad sectors" under CHKDSK or any other software.

Any defects that were present on the drive after manufacturing were reallocated by the factory LLF. Essentially, any known bad sectors are replaced by spare sectors stored in different parts of the drive. If any new defects occur, such as from a minor head/platter contact or drive mishandling, a proper IDE-aware LLF program can map the new bad sectors to other spares, hiding them and restoring the drive to what appears to be defect-free status. Because the IDE (ATA) specification is an extension of the IBM/WD ST-506/412 controller interface, the specification includes several new CCB commands that were not part of the original INT 13h/CCB support. Some of these new CCB commands are vendor-specific and are unique to each IDE drive manufacturer. Some manufacturers use these special CCB commands for tasks such as rewriting the sector headers to flag bad sectors, which in essence means LLF. When using these commands, the drive controller can rewrite the sector headers and data areas and then carefully step over any servo information (if the drive uses an embedded servo).

IDE drives can be low-level formatted, although some drives require special vendor-specific commands to activate certain low-level formatting features and defect-management options. Seagate, Western Digital, Maxtor, IBM, and others make specific LLF and spare-sector defect-management software specific to their respective IDE drives. Conner drives are unique in that to actually LLF them, you need a special hardware device that attaches to a diagnostic port connector on the Conner IDE drive.

Intelligent IDE drives must be in nontranslating, or native, mode to LLF them. Zoned recording drives can perform only a partial LLF, in which the defect map is updated and new defective sectors can be marked or spared, but the sector headers usually are rewritten only partially, and only for the purpose of defect mapping. In any case, you are writing to some of the sector headers in one form, and physical (sector-level) defect mapping and sector sparing can be performed. This procedure is, by any standard definition, an LLF.

On an embedded servo drive, all the servo data for a track is recorded at the same time by a specialized (usually laser-guided) servowriter. This servo information is used to update the head position continuously during drive function so that the drive automatically compensates for thermal effects. As a result, all the individual servo bursts are in line on the track. Because the servo controls head position, there is no appreciable head-to-sector drift, as there could be on a nonservo drive.

This is why even though it is possible to LLF embedded servo drives, it rarely is necessary. The only purpose for performing an LLF on an embedded servo drive is to perform additional physical- (sector- ) level defect mapping or sector sparing for the purpose of managing defects that occur after manufacture. Because no drift occurs, when a sector is found to contain a flaw, it should remain permanently marked bad. A physical flaw cannot be repaired by reformatting.

Most IDE drives have three to four spare sectors for each physical cylinder of the drive. These hundreds of spare sectors are more than enough to accommodate the original defects and any subsequent defects. If more sectors are required, the drive likely has serious physical problems that cannot be fixed by software.

SCSI Low-Level Format Software

If you are using a SCSI drive, you must use the LLF program provided by the manufacturer of the SCSI host adapter. The design of these devices varies enough that a register-level program can work only if it is tailored to the individual controller. Fortunately, all SCSI host adapters include such format software, either in the host adapter's BIOS or in a separate disk-based program.

The interface to the SCSI drive is through the host adapter. SCSI is a standard, but there are no true standards for what a host adapter is supposed to look like. This means that any formatting or configuration software will be specific to a particular host adapter.

Some SCSI host adapters often include the complete setup, configuration, and formatting software in the host adapter's on-board ROM BIOS. Most of these adapters also include an INT 13h interface in the BIOS.

Note:
Notice that SCSI format and configuration software is keyed to the host adapter and is not specific in any way to the particular SCSI hard disk drive that you are using.