By: Keith Turbyfill 1987
Most hard drives have bad sectors when they are new. In order to initialize the disk and lock out these bad sectors, all hard drives are pre-formatted. This pre-format is commonly referred to as a "low-level format". Later, the hard disk is partitioned with FDISK and formatted with the DOS FORMAT command. This second format is commonly referred to as a "soft format".
The low-level format is usually done when a disk is still at the manufacturer or distributor. Usually, the disk is never formatted again... but in some cases, damage to the disk, controller, or PC sometimes requires that the hard drive be reformatted. Most times, the soft format can be executed to clear the disk and make it reusable; however, sometimes the low-level format must be executed to repair the disk.
Of course, simply executing the low-level format will not always fix the hard drives problems. Other problems with the machine or serious damage to the drive can require repair or replacement of parts. The low-level format is one of several "last ditch" efforts to repair the disk before costly maintenance or replacement. NOTE: The use of the low-level format, FDISK, and FORMAT will all destroy data on the disk.
IBM has its own Advanced Diagnostics which will allow you to do (among many other things) a low-level format. Some versions of DOS have their own special utility program to low-level format hard drives (One program from Microsoft to low-level format is HSECT). With most MS-DOS and PC-DOS versions 3.0 and above, the low-level format can also be done from command level using DEBUG. The following example outlines the procedure to [1] low-level format, [2] partition (with FDISK), and [3] soft format the hard drive. This example assumes the machine has one hard drive, designated as C:
Type and enter the word DEBUG. (If you receive the error "File not found", place the supplemental DOS in the A: drive and try again.)
When DEBUG is loaded, you will be given a short dash
(-) prompt:
At this dash prompt, type and enter:
G=C800:5
The G stands for "Go", telling DOS to execute the code (or program) in the hexadecimal memory location which follows. If the machine hangs, then the release of DOS you are using probably does not support this type of low-level format or has a different starting memory location.
After you press return, you will receive a warning that you are about to destroy all data on the disk. You must enter Y to continue.
The routine will then examine the controller and determine the manner in which the switch settings (jumpers) are enabled. The total number of cylinders and heads of the hard drive (actually the number the controller is set to) will be displayed. Usually, this will be correct unless the controller or hard drive has been changed -- or the installer really screwed up. In most cases, assume it is correct and continue by answering Y.
You will then be prompted to enter the interleave factor. The interleave is the amount of space or time that the hard drive will "skip" as the head spins. High quality fast drives usually have an interleave factor of 1 or 2. Slower hard drives normally have a factor between 3 and 5. If you do not know what the manufacturer's recommended interleave is, use 3.
Next you will be prompted to enter the cylinder number and head number of the bad sectors you recorded from the hard drive label. If there where any, answer Y to continue and enter each cylinder and head. Continue until you enter all of the cylinder and head numbers listed.
When you are finished listing the bad sectors, the low-level format will proceed. When completed, you must partition the hard drive with FDISK and soft format with FORMAT.
Partitioning the Drive with FDISK
Next, run FDISK. FDISK will be contained on one of the two original DOS diskettes. Choose option [1] to create a DOS partition. Answer Y to use the entire disk for DOS. After a short pause, the program will instruct you to place the DOS program disk in the A: drive. When you press a key, the system will reboot (restart). NOTE: Different partitions can be created -- if you have a need to create several partitions (i.e. to run dual operating systems or handle a drive larger than 30 Megabytes)refer to the hard drive documentation and the DOS manual.
After you enter the correct time and date, you will be given the A> prompt. The final step is to soft format the hard drive.
Soft Formatting the Hard Drive with FORMAT.COM
From the A: prompt, type and enter:
FORMAT C:/S/V
The /S parameter causes the System to be transferred to the disk. This makes the disk bootable.
The /V parameter causes DOS to prompt you to enter a Volume label for the disk.