★ When a hard disk is functioning normally the read write head simply fly`s over the platter without making any contact.
★ These days to prevent the head from touching the platter the head are physically moved ( parked) to special areas also known as landing zones to prevent data loss.
★ The landing zones are usually areas where no data is stored.
★ Another approach is to leave the heads suspended in air so that they never come in contact with the platter surface.
★ In legacy devices the heads could not be automatically landed and in order to prevent them from touching the platter the user had to run programs manually to park the heads.
A hard drive may fail due to multiple reasons. Some of the common causes are:
★ Head Crash
★ Bad Sector
★ Circuit failure
★ Bearing and motor failure
This is caused when the read / write head comes in contact with the platter. This can cause the area where it has come in contact to lose data.
The platter in a hard drive is split into minute areas known as sectors. Sometime certain sectors might become faulty, this does not affect the entire drive.
Sometimes the head of the disk is not able to take off, it tends to stick to its position. This phenomenon is known as stiction.
After prolonged usage the hard disks motors or bearing tend to worn out hence not allowing normal disk performance.
The hard disk become inoperable if any of its circuitry malfunctions.
★ These days power consumption of electrical devices has become a prime importance as portability and performance greatly depends on a devices consumption.
★ Power consumption of a hard disk directly affects: Drive age, disk failure rates, temperatures etc.
★ Smaller drives consume less energy as compared to large drives. The disks consume maximum energy during starting up, also known as spin up.
★ Spin up and spin down is directly controlled by the SCSI controller on such drives.
There are various interfaces through which hard disks connect to the computer.
★ Legacy Bit Serial Interfaces: They are the oldest form of interfaces which used two cables to connect the disk to a controller. One cable was used for data whereas the other is used for control. In addition to the above cables a power cable was also required to provide power to the disk.
★ Modern Bit Serial Interfaces: In these types of interfaces the disk is connected to a host bus interface adapter using a single cable. In addition to this cable a power cable is also used to power the drive. Some of the modern bit serial interfaces are as follows: Fibre Channel, Serial ATA and SCSI.
★ World Serial interfaces: They are similar to modern bit interfaces, these interfaces make use of a cable for data and control. Some of the common world interfaces are as follows: IDE, EIDE, SCSI etc.