In: Root » Computers and technology » Storage Devices
A new hard disk is like a newborn babe: Although some abilities are built-in, its mind and memory are essentially blank. It has to learn about the world before it can do what it was designed for. For example, many drives must construct the individual sectors that they use for storage from the undifferentiated lengths of individual tracks. Much like floppy disk drives, the organization of a hard disk drive is called its format. Hard disks differ from floppies in that two levels of organization wear the same title-the low level format and the DOS format. Both are necessary to use a given disk under DOS, but each has its own role and requires it own procedure to set up. Older disk drive, generally those that used the ST506 (including RLL) or ESDI interfaces, allow you as the user of the disk to create or re-create the low level or physical format of the drive. In fact, these drives were often delivered without a low level format in place, requiring you to perform a preliminary low level formatting of the drive to prepare it for use. Drives with embedded servo systems which includes virtually all modern IDE, EIDE, and SCSI hard disks can only receive their low level format at the factory when they are made. The process involves special equipment and operating modes that are inaccessible in normal operation. Some early IDE drives could be rendered unusable by attempting to low level format them. Most moderns drives will refuse low level format commands or will pretend to carry out a low level format without actually altering their format. In other words, with a modern hard disk, attempting a low level format is a waste of time and runs a very slight risk of damaging the disk. Don't do it. You have no need to refresh the format of the disk as was once recommended for older drives because the media of new drives have higher retentivities and coercivities that will retain their format patterns long beyond the useful life of the drive. If you have an old drive that requires it, creating a low level format requires running a low level formatting program. Some old versions of DOS shipped with IBM-compatible computers include such a program under a name like LLFORMAT or HDPREP. Most disk diagnostic programs also include low level formatting routines. Low level formatters for pre-1987 IBM Personal Computers were included with the Advanced Diagnostics programs that IBM sold to accompany its PC and AT systems. The low level formatting program for PS/2-series machines is included on the reference disk that accompanies each computer, but it is hidden. To use this low level formatting program, boot up your PS/2 from its Reference Diskette. At the first screen, where you are asked to type Enter to continue, press the Enter key. You should then see the Main Menu, which offers you seven menu selections that you can do with the program. Ignore them. Instead, press the Ctrl and letter A keys (Ctrl-A) simultaneously. Your machine then loads its Advanced Diagnostics. You can choose the low level format routine from its two selection menu. Many of the manufacturers of aftermarket ST506 and ESDI hard disk controllers include the necessary program for low level formatting a hard disk connected to their product in the controller's ROM firmware. These routines are normally executed through the Go command of the DOS DEBUG program. For instance, a number of these routines are accessed by typing the following instruction at the DEBUG hyphen prompt: G=C800:5 If you try this with your controller and it doesn't work, you'll likely lock up your system. If it works, you'll be prompted on the screen. The built-in low level formatting routines of some vary a few bytes in position in their add-in BIOSes. You may want to try starting execution at C800:6 or C800:8 if the first example does not work. Other than locking up your computer, you won't do any damage to anything. In particular, you won't hurt any data on a new hard disk because there's nothing there to begin with! In the manufacture of hard disk platters, defects occasionally occur in the magnetic medium. These defects will not properly record data. Sectors in which these defects occur are called bad sectors; the tracks containing the sectors are called bad tracks. Modern hard disks incorporate automatic defect management. They find bad spots in their media and automatically remap them. Because the drive takes care of defect management, your PC never knows that there are bad spots on the hard disk. Your PC sees a perfect disk. Although Logical Block Addressing makes automatic defect management particularly easy, any drive with sector translation can use the technology. Only drives that use direct physical addressing cannot use this technology. These older drives that lack automatic defect management require some help from your PC. Your computer can deal with bad sectors by locking them out of normal use. During the low level formatting process, the sectors that do not work properly are recorded and your system is prevented from using them. The only ill effect of reserving these bad sectors is that the available capacity of your hard disk may diminish by a small amount. Some low level formatting programs require that you enter bad sector data before you begin the formatting process. Although this seems redundant-the format program checks for them anyhow-it's not. Factory checks for bad sectors are more rigorous than the format routine. This close scrutiny helps minimize future failure. Tedious as it is, you should enter the bad sector data when the low level format program calls for it. The listing of bad sectors is usually on a sheet of paper accompanying the disk drive or on a label affixed to the drive itself. The only time that a bad sector is an evil thing is when it occurs on the first track of the disk. The first track (Track 0) is used to hold partition and booting data. This information must be located on the first track of the disk. If it cannot be written there, the disk won't work. Should you get a hard disk with Track 0 bad, return it to the dealer from whom you bought it. If you reformat a disk after a head crash and discover Track 0 bad during the format process, you need a new disk.
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