A hard drive is a mass storage device found in all PCs (with some exclusion) that is used to store permanent data such as the operating system, programs and user files. The data on hard drives can be erased and/or overwritten, the hard drive is classed as a non-volatile storage device which means it doesn't require a constant power supply in order to retain the information stored on it (unlike RAM).
    Inside every hard drive are small round disk-like objects made of aluminum, alloy or a glass, ceramic composite, these are called platters, each platter is coated with a special magnetic coating enabling them to store data magnetically.
Hovering above these platters are read/write heads that transfer data to and from the plate, a magnetic disk where computer data is stored. The term hard is used to distinguish it from a soft, or floppy, disk. Hard disks hold more data and are faster than floppy disks. A hard disk, for example, can store anywhere from 10 to more than 100 gigabytes, where as most floppies have a maximum of 1.4 megabytes. For example, a typical 84 megabyte hard disk for a PC might have two platters (four sides) and 1,053 cylinders.
    A single hard disk usually consists of several platters. Each platter requires of two read/write heads, one for each side. All the read/write heads are attached to a single access arm so that they cannot move independently. Each platter has the same number of tracks, and a track location that cuts across all platters is called a cylinder.

What's Inside a Hard Drive?

    All hard drives share a basic structure and are composed of the same physical features. However, not all hard drives perform the same way as the quality of the parts of the hard drive will affect its performance. Following is a description of the common features of the hard drive and how each part works in relation to the others. Hard drives are sensitive equipment and the internal workings of a hard drive it should not be handled by anyone rather than an experienced professional.

The Platters

    The platters are the actual disks inside the drive that store the magnetized data. Traditionally platters are made of a light aluminum alloy and coated with a magnetic material such as a ferrite compound that is applied in liquid form and spun evenly across the platter or thin metal film plating that is applied to the platter through electroplating, the same way that chrome is produced. Newer technology uses glass and/or ceramic platters because they can be made thinner and also because they are more efficient at resisting heat. The magnetic layer on the platters has tiny domains of magnetic that are oriented to store information that is transferred through the read/write heads. Most drives have at least two platters and the larger the storage capacity of the drive, the more platters there are. Each platter is magnetized on each side, so a drive with 2 platters has 4 sides to store data.

The Spindle and Spindle Motor

    The platters in a drive are separated by disk spaces and are clamped to a rotating spindle that turns all the platters in unison. The spindle motor is built right into the spindle or mounted directly below it and spins the platters at a constant set rate ranging from 3,600 to 7,200 RPM. The motor is attached to a feedback loop to ensure that it spins at precisely the speed it is supposed to.

The Read/Write Heads

    The heads read and write data to the platters. There is typically one head per platter side, and each head is attached to a single actuator shaft so that all the heads move in unison. When one head is over a track, all the other heads are at the same location over their respective surfaces. Typically, only one of the heads is active at a time, i.e., reading or writing data. When not in use, the heads rest on the stationary platters, but when in motion the spinning of the platters create air pressure that lifts the heads off the platters. The space between the platter and the head is so minute that even one dust particle or a fingerprint could disable the spin. This necessary that hard drive assembly be done in a clean room. When the platters cease spinning the heads come to rest, or park, at a predetermined position on the heads, called the landing zone.

The Head Actuator

    All the heads are attached to a single head actuator, or actuator arm, that moves the heads around the platters. Older hard drives used a stepper motor actuator, which moved the heads based on a motor reacting to stepper pulses. Each pulse moved the actuator over the platters in predefined steps. Stepper motor actuators are not used in modern drives because they are prone to alignment problems and are highly sensitive to heat. Modern hard drives use a voice coil actuator, which controls the movement of a coil toward or away from a permanent magnet based on the amount of current flowing through it. This guidance system is called a servo.
The platters, spindle, spindle motor, head actuator and the read/write heads are all contained in a chamber called the head disk assembly (HDA). Outside of the HDA is the logic board that controls the movements of the internal parts and controls the movement of data into and out of the drive.
Landing zone- A non-data space on a computer's hard disk where the read/write heads rest, or park, when the computer's power is turned off.

Clean room
 

    A work area in which the air quality, temperature and humidity are highly regulated in order to protect sensitive equipment from contamination. Clean rooms are important features in the production of silicon chips, hard disk drives and other technologies such as satellites. The air in a clean room is repeatedly filtered to remove dust particles and other impurities that can damage the production of highly sensitive technologies.
    The measure of the air quality of a clean room is described in Federal Standard 209. Clean rooms are rated as "Class 10,000" where there exist no more than 10,000 particles larger than .5 microns in any given cubic foot of air, "Class 1000," where there exists no more than 1000 particles; and "Class 100," where there exist no more than 100 particles. Hard disk drive fabrication requires a Class 100 clean room. People who work in clean rooms must wear special protective clothing called "bunny suits" that do not give off lint particles and prevent human skin and hair particles from entering the room's atmosphere. When installing a hard disk drive (commonly called a hard drive) for the first time, attempting to remove errors from your drive, getting rid of a nasty virus, or even cleaning a hard drive because you are selling or donating your computer -- those are just a few of the many reasons why one might consider formatting their hard drive. Format actually means to prepare a storage medium, usually a disk, for reading and writing. When you format a disk, the operating system erases all bookkeeping information on the disk, tests the disk to make sure all sectors are reliable, marks bad sectors (that is, those that are scratched or otherwise damaged), and creates internal address tables that it later uses to locate information. You must format a disk (floppy or hard disk) before you can use it. When you take a disk that has been formatted and run it through the format process again, it is referred to, logically, as "reformatting".

Key Steps to Formatting

    Back it up! Before the format process, you want to make sure that if your goal is hard drive recovery, you back up as much personal data and information from your hard drive as you need. In some instances where a virus has caused serious system damage, this may not be possible, but if your format is planned ahead of time you certainly can copy and archive data off your hard drive before you start the format process.

 

How to Format
 

    If you purchased your computer from systems vendor such as a Dell, HP Compaq or Gateway system, you most likely will have a set-up or a restore-and-recovery CD (also referred to as a master CD) which came with the system. If this is the type of system you use, then a format is an easy process as the master CD will format the hard drive, reinstall your Windows operating system, and install any software and programs which came with the system. If you no longer have your master set-up CD, you should contact the manufacturer to get a replacement.
If you aren't using this type of mass-market system, then a hard drive format will consist of you formatting the hard drive manually, installing your Windows OS from CD, then installing your software programs and hardware drivers. Before you begin the formatting process, it is important to make sure you have your entire driver CDs located, Windows CD and your software CDs to ensure a smooth set-up.
    It's also important to know about your operating system before you format. For example, if you're going to be reinstalling Windows 98 or Windows Me then you should have a Windows 98 or ME start-up disk to complete the procedure. In this instance, you would restart the system with the start-up floppy in the drive. Upon system boot, you will choose to have CD-ROM support. Once the files load you can then choose to run the format command on your main drive (usually C drive). If you are using Windows 2000 or Windows XP, the Windows installation process offers "format your hard drive" as an option. Here you would ensure your computer is set to boot from CD-ROM (a setting in your system BIOS), insert the Windows CD and restart the computer. From there you will be on your way to reformatting.

The Format Command

 

    Format is a Microsoft DOS command. It's a command line you can run to remove information from a computer disk, floppy disk or hard disk. It is an external command found in many of the Windows Operating systems. Hard drive formatting is done in three steps:

- Low-level formatting creates the physical structure on the hard drive. Partitioning divides the hard drive into logical pieces that become volumes. High-level formatting defines the logical structures on the partition and places at the start of the disk any necessary operating system files. The format command syntax is the following:
FORMAT drive: [/parameters]
- Where drive: specifies the volume to format (the hard disk letter followed by a colon) -example format c:
-where [parameters] formats the disk with different options — example format c: /s will copy system files to the formatted disk or format c: /q performs a quick format.
-The syntax used between Windows 95, 98 and ME differ slightly from Windows 2000 and XP. To see the available Format command parameters for your operating system, you can type FORMAT /? At the DOS command line.

Does Formatting Really erase All Data?
 

    It's important to remember that "format" and "delete" do not mean erase! Reformatting a disk does not erase the data on the disk, only the address tables. The good news is that if you accidentally reformat a hard disk, a computer specialist should be able to recover most or all the data that was on the disk. The bad news is that for any business or corporation that is planning to donate old computers to charity, this could pose a security risk if that computer disk drive contained confidential business information. Remember — just because you may donate the computer to charity that doesn't mean an honest person will end up with it. While that shouldn't deter you from recycling old computers in this way, it should be an incentive to ensure all business data has been completely wiped from the hard drive. Never just delete the files and assume they are gone because you can't see them on the hard drive. Businesses should at the very least run the format command to erase the hard drive. The safest method to completely remove data is to overwrite the disk. You can do this yourself, although it is quite time consuming. To overwrite the disk would mean to format, then fill the disk completely with data, and format again. The easiest way to do this is to use a software program that will overwrite the disk for you. Most of these programs, which are often referred to as "Data Dump" software, will meet even the strict deletion requirements of the U.S. military. As an added bonus, a few good data dump programs can be freely downloaded from the Internet.