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IDE Low-Level Format Software

IDE drive manufacturers have defined extensions to the standard WD1002/1003 AT interface, which was further standardized for IDE drives as the ATA (AT Attachment) interface. The ATA specification provides for vendor-unique commands, which are manufacturer proprietary extensions to the standard. To prevent improper low-level formatting, many of these IDE drives have special codes that must be sent to the drive to unlock the format routines. These codes vary among manufacturers. If possible, you should obtain LLF and defect-management software from the drive manufacturer; this software usually is specific to that manufacturer's products.

The custom nature of the ATA interface drives is the source of some myths about IDE. Many people say, for example, that you cannot perform an LLF on an IDE drive, and that if you do, you will wreck the drive. This statement is untrue! What can happen is that in some drives, you may be able to set new head and sector skew factors that are not as optimal for the drive as the ones that the manufacturer set, and you also may be able to overwrite the defect-map information. This situation is not good, but you still can use the drive with no problems provided that you perform a proper surface analysis.

Most ATA IDE drives are protected from any alteration to the skew factors or defect map erasure because they are in a translated mode. Zoned recording drives always are in translation mode and are fully protected. Most ATA drives have a custom command set that must be used in the format process. The standard format commands defined by the ATA specification usually do not work, especially with intelligent or zoned recording IDE drives. Without the proper manufacturer-specific format commands, you will not be able to perform the defect management by the manufacturer-specified method, in which bad sectors often can be spared.

Currently, the following manufacturers offer specific LLF and defect-management software for their own IDE drives:

• Seagate • Maxtor
• Western Digital • IBM

Nondestructive Formatters

General-purpose, BIOS-level, nondestructive formatters such as Calibrate and SpinRite are not recommended in most situations for which a real LLF is required. These programs have several limitations and problems that limit their effectiveness. In some cases, they can even cause problems with the way defects are handled on a drive. These programs attempt to perform a track-by-track LLF by using BIOS functions, while backing up and restoring the track data as they go. These programs do not actually perform a complete LLF, because they do not even try to LLF the first track (Cylinder 0, Head 0) due to problems with some controller types that store hidden information on the first track.

These programs also do not perform defect mapping in the way that a standard LLF programs do, and they can even remove the carefully applied sector header defect marks during a proper LLF. This situation potentially allows data to be stored in sectors that originally were marked defective and may actually void the manufacturer's warranty on some drives. Another problem is that these programs work only on drives that are already formatted and can format only drives that are formattable through BIOS functions.

A true LLF program bypasses the system BIOS and send commands directly to the disk controller hardware. For this reason, many LLF programs are specific to the disk controller hardware for which they are designed. It is virtually impossible to have a single format program that will run on all different types of controllers. Many hard drives have been incorrectly diagnosed as being defective because the wrong format program was used and the program did not operate properly.

Drive Partitioning

Partitioning a hard disk is the act of defining areas of the disk for an operating system to use as a volume. To DOS, a volume is an area of a disk denoted as a drive letter; for example, drive C is volume C, drive D is volume D, and so on. Some people think that you have to partition a disk only if you are going to divide it into more than one volume. This is a misunderstanding; a disk must be partitioned even if it will be the single volume C.

When a disk is partitioned, a master partition boot sector is written at Cylinder 0, Head 0, Sector 1 — the first sector on the hard disk. This sector contains data that describes the partitions by their starting and ending cylinder, head, and sector locations. The partition table also indicates to the ROM BIOS which of the partitions is bootable and, therefore, where to look for an operating system to load. A single hard disk can have 1 to 24 partitions. This number includes all the hard drives installed in the system, which means that you can have as many as 24 separate hard disks with one partition each, a single hard disk with 24 partitions, or a combination of disks and partitions such that the total number of partitions is no more than 24. If you have more than 24 drives or partitions, DOS does not recognize them, although other operating systems may. What limits DOS is that a letter is used to name a volume, and the Roman alphabet ends with Z — the 24th volume, when you begin with C.

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