Hard disk, Components, Characteristics, Performance and Hard disk controllers

The hard disk is a type of magnetic disk. It is also called a fixed disk because it is fixed in the system unit. A hard disk consists of several circular disks called platters sealed inside a container. The container contains a motor to rotate the disk. It also contains an access arm and read and write head to read and write data to the disk. The platters are used to store the data. A platter in a hard disk is coated with magnetic material.

hard disk parts
Figure: Hard disk 

The hard disk used in computers spin at the speed of 5400 to 15000 revolutions per minute. The speed at which the disk spins is a major factor in its overall performance. The high rotational speed allows more data to be recorded on the disk surface.

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.

 Hard disk performance

       The following factors affect the performance of the hard disk:

Seek time:  it is also called positioning performance. It is the time required by reading and writes head to the correct location on the disk.it is often used with rotational speed to compare the performance of hard drives. It is measured in milliseconds.

Spindle speed: it is also called transfer performance. It is the speed at which the driver transfers the data.

Latency: it is the time required by the spinning platter to bring the desired data to read and write head.

External and Removable Hard Disks

      An external hard disk is a separate hard disk that is connected to the USB port on the CPU. Some hard disks can also communicate with the system unit wirelessly.

A remove able hard disk is a type of hard disk that can be connected to the system unit using the USB port or firewire port.

There are some advantages to removable hard disks as follows:

  1. These can be used to transfer a large number of files from one place to another place.
  2. These can be used to back up important files.
  3. These can be used to store a large number of audio, and video.

Miniature hard disks

      These disks are very small hard disks. These disks are available in a different size. The devices such as portable and smartphones have miniature hard disks. These

It provides more storage capacity than flash memory.       

Hard disk controllers

It consists of chips and electronic circuits. It also controls the transfer of data, instructions, and information between system and system unit.

           There are 4 types of hard disk interfaces for personal computer which are as follows:

1: SATA        

                  SATA stands for serially advanced technology attachment. It used for serial signals to transfers data, instruction and information. The main advantage of SATA is that cables are thinner, longer and higher. The external hard disks can use the SATA interface that is much faster than USB.


             EIDE stands for Enhanced Integrated Drive Electronics. EIDE is a device interface that used signals parallelly to transfer the instructions and data etc. The approximate data transfer speed of EIDE is up to 133 Mbps.


             SCSI stands for Small Computer System Interface. It is used as a parallel signal and cannot support from 8 to 15 devices. SCSI can support hard disks, disk drives, printers, etc.

4: Disk cache

                      It is used to improve hard disk performance.it is a type of ram program instructions and data that the user is working with. When the CPU needs the information it first looks at the cache from the hard disk and if it doesn’t need the information it retrieves information from the hard disk.

Difference between SATA and HDD

What is SATA?

SATA stands for Serial Advanced Technology Attachment. SATA is used for transferring data from hard disk drives to computer systems. SATA is a point of interface for communication with other storage devices like disk drives, optical drives, SSD etc. The cables of SATA are thinner and flexible.SATA has many advantages over the hard drive.

Advantage of SATA

  • SATA Cables are flexible and thinner
  • The transfer rate of SATA is very high than HHD.
  • It is very easy to manage cables length.
  • SATA manages RAID in an efficient way.
  • It provides an internal-external interface.
  • It is equipped with NCQ (Native Command Queuing)

SATA does not have jumper cables and due to this no fussing with Master/slave/cable select setting

Disadvantages of SATA

  • Sate drives can be used only in an IDE.
  • The computer can only use a cheap SATA to IDE reversible interface.
  • if the cable length is too long, serial devices driven at high speed can be subject to interference

What is HDD?

In all PCs, the traditional hard disk used as a storage device. A typical hard drive contains a circular disc called platter used to store data. The disc rotates, allowing the read-write arm to read data on the disc and write data to tithe working of platter affect the performance of hard disk like The faster the platter spins, the faster the hard drive works, which can depend on how quickly your operating system responds, and how long it takes applications installed on the drive to load and open. The Older hard drives use an IDE port to connect to the motherboard of a PC, but now many modern hard drives use a SATA connection. The new version of SATA, SATA III, is found on modern motherboards, and able to the fastest possible data transfers for an HDD.

Advantages of HDD

  • It has a large capacity for storing data
  • It is much faster than optical disks like DVD’S
  • It has Persistent storage
  • HDD easily replaced and upgraded.

Disadvantages of HDD

  • It depends upon on moving parts
  • The disk surface can be damaged easily.
  • It consumes heavy power.
  • It makes more noise.
  • Its read/write speed is slower than RAM.

Comparison of HDD versus SSD

Stands forSolid State DriveHard Disk Drive
Heat, Electricity and NoiseLess rotation required.

Uses less power.

Less heat or noise.

More heat generation.

More noise.

More electricity to rotate the platters.


SpeedSSD has lower latency

SSD has faster read/writes

SSD has supports more input output operations per second.


HDD  supports fewer input output operations per second.

HDD has higher latency

HDD has longer read/write times


ComponentsSSD architecture have NO moving parts.HDD architecture have moving parts.
DefragmentationPerformance don’t care about  fragmentation.

Defragmentation is not compulsory as in HDD.

The performance is not better and the main reason is disk  fragmentation. We need frequent defragmentation.
WeightLess in weight.Heavy in weight.

Frequently Asked Questions (FAQ)

Is a 256gb SSD better than a 1tb hard drive?

Suppose we have a laptop with a 128GB or 256GB SSD instead of a 1TB or 2TB hard disk . A 1TB hard disk storage is equal to 8 times 128GB SSD, and similarly 4 times as much as a 256GB SSD.

You must also know about

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Prof. Fazal Rehman Shamil
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