Sarasota PC Monitor
Tech Talk(11/98)
Whys and wherefores of formatting hard drives
by Brian K. Lewis, Ph.D.*
Member of the Sarasota Personal Computer Users Group, Inc.Anyone who has used a computer soon becomes familiar with the term "formatting." However, few users understand the reason for this process. As a result, I frequently hear people talk about reformatting their hard drive because something was giving them trouble. Usually, reformatting is unnecessary and it may create more problems than it solves. So let's look at what happens to a hard drive in the factory formatting process and then the format done by the operating system. Both processes are necessary to allow the drive to be used in your computer.
First, we need to have an understanding of the structure of the drive. Hard drives have one or more circular platters (disks) that rotate on a common spindle. The surfaces of these platters are coated with a magnetic media. Each surface has its own read/write head that floats just over the surface when the drive is running. All of the heads are connected to the same control so all move simultaneously. Both floppy disks and hard drives are manufactured with concentric rings or tracks on the platters.
In order for the computer to find information stored on these disks easily, areas must be numbered or identified. This is done by dividing each track into numbered sectors. Each sector has a prefix region, a data region and a suffix region. On most hard disks the sector stores 571 bytes of which 512 bytes are in the actual data region. The identification for the sector is stored in the prefix region and is written to the hard disk in the factory formatting process, the low-level format. This formatting process also has to allow for gaps between the sectors and between tracks. The factory formatting software writes to the data area of each sector and to the suffix. This write/read process provides a basis for finding and marking bad sectors.
Originally, all hard drives had to use a specified number of sectors per track because the drive controllers were separate from the drives and could be from other manufacturers. That way anyone could carry out a low-level format on hard drives. In fact, most drives purchased from a wholesaler had to be low level formatted when first installed. Today's IDE and SCSI drives have their controllers built into their electronics. This includes program extensions to the original drive specifications and includes the capability of responding to vendor-unique commands. In addition, the newest drives use zoned bit recording in which the number of sectors per track is highly variable. As a result, most new drives now have more sectors per track in the outer tracks than on the inner tracks. One newer IDE drive for example, has 232 sectors in the outermost track and 122 in the innermost track. This design affects the rate of data transfer. Data can be read or written to the outer track at a rate of just over 10 Mbytes per second. In the inner tracks the rate is just over 5 Mbytes per second. Because of the variable nature of the sector/track relationship and several other mechanical factors, manufacturers generally do not recommend that hard drives be low level formatted except at the factory. Any such formatting may reduce the drives' storage capacity and data transfer rates. The newest drives, using zoned bit recording, cannot be low level formatted after they leave the factory unless the software used sends the proper codes to unlock the formatting routine. So it is important that drives be low-level formatted only with software supplied by the manufacturer. Even then there may be a reduction in drive efficiency and/or rate of data transmission.
Once the drive has the track sector information written to it, it can be partitioned and high level formatting can be done. The partition information was originally designed to allow different operating systems to be installed on a single hard disk. Then as disk sizes increased, it became advantageous to partition a drive to reduce the number of sectors used for the minimum file size. Although the "A" version of Windows 95 can support drives of up to 2.GB capacity, the minimum file size with a single partition is 32KB. By dividing the drive into several partitions, this can be reduced to 8KB, a significant saving in hard disk space. Under Windows 98, using the 32-bit FAT system, you can install a single partition on drives up to 8GB capacity and have a 4K minimum file size. That is a considerable improvement.
The final step in preparing a hard drive for use is the high level format using the operating systems format command. The primary function of this program is to set up the directory system for the drive. During the first scan of the hard drive, the format program looks for bad sectors, especially those marked by the low-level format. Any that are found are identified in the FAT or file allocation table. This prevents the operating system from attempting to write data to these areas. The high level format writes boot sector information to the first sector of the drive. If the "/s" command was specified, it will also write the boot files to this location. In the second sector it will write the first FAT and immediately after this the second FAT. These FATs are essentially empty except for any bad sector information that has been collected. The format program will also write a blank root directory. This format process does not alter the sector identification or write to any other data areas.
Obviously the process of preparing a hard drive is quite extensive. That used for floppy disks is similar, except that floppy disks are low-level formatted and high level formatted in one step. This explains the quick format option for floppies that can be found in Windows 9x. The quick format simply uses an erase process that alters the information in the FAT. It does not rewrite all the sector information to the disk. This speeds up the format process considerably.
So what does all this information mean and why bother to consider it? When you are troubleshooting problems with a computer the least likely source of problems are hard drive read/write errors. Unless you are getting "sector not found" errors or ScanDisk is reporting increasing numbers of bad sectors, you should not consider the hard disk as being the problem. An inability to read a single file or run an application does not suggest that the drive should be reformatted. Instead, the best remedy is to delete the file or application, run ScanDisk to see if any sectors have gone bad and should be marked. This determination will be done automatically by ScanDisk. If you are getting sector errors, then the drive should probably be replaced as only a low-level format can generally solve this problem. The drive also becomes the problem when mechanical failures become apparent. The drive starts to talk louder (or even scream) or you start getting grinding noises. These are indications of impending drive failure and mean you will have to replace the drive. It is not likely that a reformat at any level will solve the problem.
The point I am trying to make is that too often we leap at reformatting a hard drive to solve problems that are being caused by application software. The better solution is to remove an application completely. Then do a clean reinstall from the original application disks. Your backup might include the problem you trying to solve, especially if the problem is associated with the registry. It is rare that reformatting a drive is necessary and even rarer that it really solves the problem. It is the software reinstallation in a clean environment that can actually solve the problem.
*Dr. Lewis, a former university & medical school professor, is currently a computer consultant and part-time computer instructor for Sarasota County Technical Institute. He is available, on a fee basis, to help you with your home or business computer problems. He can be reached via e-mail at bklew@worldnet.att.net or voice mail at 941/925-3047. :
Copyright 1998. This article is from the November 1998 issue of the Sarasota PC Monitor, the official monthly publication of the Sarasota Personal Computer Users Group, Inc., P.O. Box 15889, Sarasota, FL 34277-1889. Permission to reprint is granted only to other non-profit computer user groups, provided proper credit is given to the author and our publication. We would appreciate receiving a copy of the publication the reprint appears in, please send to above address, Attn: Editor. For further information about our group, email: admin@spcug.org/ Web: http://www.spcug.org/
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