A hard disk is a storage device that makes use of the magnetization of particles to save data on its surface. A hard disk is also known as a hard drive. The data is stored in a hard disk drive in the form of a magnetic pattern. The hard disk drive was invented by a team of people working at the American computer manufacturing company known as IBM or International Business Machines Corporation in the year 1956. Rey Johnson led the team, which is why he is also known as the father of disk drives. The first hard disk was launched by IBM on September 13, 1956. Initially, the hard disk drives were capable of storing a limited amount of data and were bulky in size; however, with improvisation in the technology the data storing capacity of the drives was enhanced and the size of the devices was effectively reduced. The maximum amount of data that a hard disk drive is capable of storing to date is equal to 18 Terabytes. A hard disk drive is capable of storing all types of data such as images, audio files, text documents, etc. It can support the storage of a variety of file formats such as jpeg, png, WAV, mp3, mp4, MKV, WEBM, and many more. Hard disk drives are advantageous as they have a longer life span as compared to other data storage devices and are readily available in the market at affordable prices. Also, they have a better data storing capacity than other devices such as SSDs. The limitations of hard disk drives include heavy power consumption, high cost, and noise produced during usage. As compared to RAM, a hard disk allows a slow rate of transferring and accessing the data. The hard disk drives need to be handled carefully as even a minor crack on the surface can cause rupturing of the device and loss of data.
Working Principle of a Hard Disk
A hard disk typically works on the principle of simple magnetism to store the data and information. A hard drive typically consists of a large plate that is usually made up of a magnetic material and is known as a platter. The platter is usually constructed in a circular shape. The surface of the magnetic plate is divided into billions of tiny compartments. The magnetization of the tiny areas can be performed independently. Magnetized tiny area of the plate denotes a binary high and is equivalent to binary value one; whereas, the demagnetized tiny area denotes a binary low and is equivalent to binary value zero. This indicates that the letters, numbers, and other forms of data stored by the hard disk drive are a combination of binary values, i.e., zeroes or ones. The smallest portion of the information stored by the hard disk drive is known as a bit. The process of magnetization of materials is typically preferred to store information in the disks as it does not get affected by switching off the power supply. The data is retained by the drive even if it is not connected to the power supply for a long time period. The magnetised portion of the hard disk tends to stay magnetized until it is externally demagnetised, thereby allowing reliable storage of data.
Components of a Hard Disk
A hard disk drive typically consists of 9 major components, namely an actuator, a read-write arm, a central spindle, a magnetic platter, a plug, a read-write head, circuit board, a connector, and a small spindle.
The actuator is a simple device that helps in the conversion of electrical energy into mechanical energy. Here, the main purpose of the actuator is to drive the read-write arm. Initially, stepper motors were typically used by the hard drives to move the read-write arm, but they were soon replaced by the actuators as stepper motors move at a comparatively slower rate, are less reliable, lack precision, and are much more sensitive to physical parameters of the environment such as temperature, pressure, etc. In some of the latest versions of hard disk drives, voice coils are used in the place of actuators.
2. Read-Write Arm
The read-write arm acts as a driving mechanism that moves the read-write head over the surface of the platter in a back and forth direction.
3. Central Spindle
The spindle attached to the centre of the platter holds the device in place and helps in the uniform rotation of the disk at a considerably high speed along its axis.
4. Magnetic Platter
A magnetic platter is a circular disk that is typically made up of aluminium or glass and has a magnetic coating applied on its surface. It is one of the most important parts of a hard disk drive. The magnetic platter of a hard disk is mainly responsible for the storage of data with the help of the magnetisation process. A hard disk drive consists of a number of magnetic platter disks that are stacked on top of one another and are mounted on a common spindle. The rotation per minute of the platter is directly proportional to the speed of operation of the device.
The plug of the hard disk helps to connect the hard disk drive to a computer system.
6. Read-Write Head
The read-write head is a small piece of a magnet attached to the top of a read-write arm that performs the main task of reading data from the hard disk and writing the data on the surface of the platter. A hard disk drive typically consists of two read-write heads for each platter disk. One of the heads is attached to the top of the platter, whereas, the other is placed in close contact with its base. This enables the device to access data available on both sides of the platter. To protect the device from excessive wear and tear, the read-write head is made to hover over the surface and a layer of fluid or air is inserted between the read-write head and the platter.
7. Circuit Board
The circuit board of a hard disk drive is usually made up of aluminium, glass, or ceramic material. It is embedded in the internal circuitry of the hard disk drive and is used to circulate the data contained by the disk by controlling the flow of data to and from the magnetised platter.
8. Flexible Connector
The flexible connector attached to the internal mechanism of the hard disk drive near the platter is mainly used to carry data from the circuit board to the read-write head of the device and vice versa.
9. Small Spindle
A small spindle is attached to the side of the machinery that helps the read-write arm of the device to swing sideways over the magnetised platter.
Working of a Hard Disk
A hard drive consists of a stack of disks or platters that spin at a significantly high speed. A recording head is typically attached to the top and the bottom portion of each platter. A layer of microscopic magnetized metal grains is applied to the surface of the disks. The main purpose of the coating of magnetized metal grains present on the surface of disks is to form magnetic patterns to hold the information or store the data. For this purpose, the grains tend to arrange themselves in the form of groups. Here, each group formed by the grains is known as a bit. The two states in which the magnetization of the grains can be achieved denote the binary bits 0 and 1. The data is stored on to the disk by converting digital data or the binary combination of bits into analogue data or the electric current. The transfer of bits takes place with the help of an electromagnet that is attached to the internal mechanism of the hard drive. The magnetic field generated by the electromagnet is highly intense and is capable of reversing or changing the direction of magnetization of the metal grains. To retrieve the information stored on the drive, a magnetic reader is used. The information that is stored on the surface of the hard disk drive is arranged in a specific order. The data bits containing the information are arranged in concentric circular paths. These paths are known as tracks. The tracks can be further divided into smaller areas known as sectors. Whenever the user provides a command to save the data, the read-write head of the device tries to locate the free sectors of the platter and establish magnetisation and demagnetisation of the magnetic grains present in that particular area according to the input signal. A portion of the hard disk drive is specifically dedicated to keep a track of the free and used up portions of the drive. The map that displays the usage of the drive is known as the file allocation table or FAT. When the user provides a command to the computer to save information on the surface of the disk, then the computer approaches the file allocation table to find the appropriate place required to save the data. Once the suitable place is located by the computer, the read-write head is made to move on the surface of the platter accordingly. Finally, the grains present on the surface of the disk get magnetized and demagnetized as per the input data, and the data is successfully saved. To read the data or to retrieve back the saved information, the process gets reversed. A hard disk drive is susceptible to losing data if the particles of foreign material such as dust particles, moisture molecules, etc. manage to enter the internal circuitry of the device, which is why a backup of the data stored into a hard disk is usually preferred. This means that a hard disk is a delicate device that requires proper and careful handling.