What
is HDD
HDD is an electro-mechanical storage device, which is an
abbreviation of Hard Disk Drive. It uses magnetic storage for storing and
retrieving the digital data. It is a non-volatile storage device.
Hard Disk Drive is installed internally in our computer
systems, which is connected directly to the disk controllers of the
motherboard. Hard Disk Drive is a storage device which stores the operation
system (OS), installed software, and the other computer files.
HDD means the data is retained when our computer system
is shut down. HDD is also called a fixed disk, hard disk, or hard drive. The
HDD was introduced in the year 1956 by IBM.
The first personal computer contains a hard drive of less
than 1 megabyte, while modern computers contain the hard drive of 1 terabyte.
The desktop computers which have external hard drives are used for backup
purposes or additional storage.
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 magnetized portion of the hard disk
tends to stay magnetized until it is externally demagnetized, 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.
1. Actuator
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 center 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 aluminum 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 magnetization 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.
5. Plug
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 aluminum, 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 magnetized 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 magnetized 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 magnetization and demagnetization
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.
Characteristics of Hard
Disk
Some important characteristics of the
hard disk are as follows:
- The hard disk provides a large storage capacity. The capacity of a personal computer hard disk is from 160 GB to 2TB and more.
- It is much faster than the floppy disk.
- It is the primary media for storing data and programs.
- It is more reliable than a floppy disk.
- Data stored on the hard disk is safer than the floppy disk.
Advantages of Hard Disk Drive (HDD)
Following are the advantages of Hard Disk Drive:
- One of the significant advantages of a Hard Disk drive is that its cost is low.
- Another advantage of Hard Disk Drive is that it is readily available in the market.
- Hard Disk Drives are faster than the optical disks.
- The capacity for storing the data in HDDs is large.
Disadvantages
of Hard Disk Drive (HDD)
Following are the disadvantages or limitations of Hard Disk Drive:
- The speed of reading and writing in HDD is slower than the RAM.
- HDDs are noisy.
- Another disadvantage of HDD is energy inefficiency.
- HDDs consume more power.
- The form factor of HDDs is heavier than the SSDs.
