A low-level format performs three simultaneous functions:
It creates and organizes the sectors, making them ready to accept data.
It sets the proper interleave (records the sector header, trailer information, and intersector and intertrack gaps).
It establishes the boot sector.
Every hard disk drive arrives from the factory with bad spots on the platters. Data cannot be written to these areas. As the sectors are being created, the low-level format attempts to skip over these bad spots. Sometimes, it is impossible to skip over a spot so the sector is marked as "bad" in the ID field.
Low-level formatting is not required on IDE and U-DMA drives. Performing a low-level format on these devices might render the drive unusable. SCSI drives are low-level formatted using a utility that is built into the SCSI adapter card's firmware. Format a low-level drive only if it is absolutely necessary (for example, if a virus has contaminated the boot sector and that is the only remedy) and if you are sure you know and can follow the proper procedure! Remember, as soon as you issue the format command, all data on the drive will be lost.
IDE drives use a special type of low-level formatting called embedded servo. This type of low-level formatting can be done by the manufacturer only, or with a special utility provided by the manufacturer. When installing an IDE drive, go straight to the partitioning step after the CMOS is set up.
To continue with hard disk drive installation for MS-DOS and Windows 3.x and 95 and 98 versions, you will need a bootable floppy disk containing several programs that are required to prepare the new drive. (For Windows NT and 2000, alternate methods that are not part of the current A+ test are available. You can also use the procedure listed below to prepare a drive for use with those operating environments.)
To create a bootable floppy disk, a computer is required that has an installed working hard disk drive, or floppy disk drive, and a compatible operating system. Be sure to use the same operating system on the floppy disk as the one you'll use for the new drive.
Insert a floppy disk into the A drive and type:
format a: /s
This will copy system files to the disk, making it a bootable disk.
The next step is to copy the necessary files from the MS-DOS directory to the floppy disk. The default location for these files is the C:\DOS directory for MS-DOS and the C:\Windows\Command directory for Windows 95 and 98. Copy these files:
format.com (or format.exe) fdisk.com
This bootable disk can be used for partitioning and high-level formatting as discussed in the following sections.