What are storage devices?

Storage devices can store digital information/data and applications (in the form of audio, video, image, etc.) to process the result of any computational work. They are a kind of computer hardware that stores information and instruction to be processed. A storage unit is a part of a computer system. Every computer has a storage device. The storage devices work as a memory. They are also known as a storage medium, digital storage, or storage media, which temporarily or permanently store information. They are used either internally or externally in the computer system, server, or any computation device to hold the information. Examples include a pen drive, CD, DVD, floppy disk, memory card and so forth.

Example of storages devices
Storage devices

Types of computer storage

There are three types of computer storage which are listed below.

1. Primary storage

Primary memory is also known as the main memory, and it is directly accessible by the computer's CPU (Central Processing Unit). It is a volatile memory, and it is temporary storage. It means that the memory is erased when the computer device is turned off or rebooted. This storage device fits internally in the computer. For example, RAM and Cache Memory (both are computer internal memory). It provides fast service in terms of accessing data files. It is small in size.

2. Secondary storage

Secondary storage device is not directly accessible by the CPU. Examples include USB storage devices, optical disk drive, floppy disk, hard drive, SSD, flash memory, etc. A secondary storage device stores data permanently until the data is removed by an external factor. It includes both internal and external memory.

It is non-volatile and has a larger storage capacity than primary storage.

3. Tertiary memory

The primary goal of the tertiary storage level is to provide massive store capacity at a cheap cost. Tertiary storage consists of large-capacity data archives that may accommodate a large number of removable media, such as tapes or optical discs.

Computer storage devices

Four types of devices are available in which computers store data. They are as follows:

1. Magnetic storage devices

These are commonly used devices, which store a large amount of data through the magnetized medium and are easily accessible by the computer system. An example of a magnetic disk drive is a hard drive.

Hard drive

A hard drive is also referred to as a Hard Disk Drive (HDD). These are directly connected to the computer's motherboard disk controller. Hard disks are flat circular plates made of aluminum or glass coated with magnetic materials. A hard drive has a large storage capacity and stores and retrieves data much faster than a floppy disk or CD/DVD.

An image of a hard disk drive
Hard Disk Drive

2. Optical storage devices

Optical storage devices use lasers and lights to store the information/data, which means the data is read and written with a laser. Examples of optical devices are Compact Disk Read-Only Memory (CD-ROM), Digital Versatile Disk Read-Only Memory (DVD-ROM), Digital Versatile Disk Random-Access Memory (DVD-RAM), Write-Once, Read-Many (WORM), CD-R, CD-RW, Blu-ray Disc Recordable (BD-R), Blu-ray Disc Recordable Erasable (BD-RE), BD-ROM, etc.

3. Flash memory devices

Flash memory devices replace magnetic and optical storage devices. These devices are easy to use, portable and readily accessible. It is a non-volatile memory chip that stores data. It can be used to transfer data from one device to another. It is a plug-and-play device. Examples include USBs, solid-state drives (SSD) and so forth.

USB (Universal Serial Bus)

USB drives also known as pen drives. It is a secondary storage device. It is used to attach printers, mouse, keyboard and other wireless devices to the computer. The storage capacity range of USB is 2GB to 1TB and it is smaller in size.

Image of a pen drive
Pen Drive

Solid-state drives (SSD)

Solid-state drives are non-volatile memory devices. They store data on solid-state flash memory. A traditional hard drive has a spinning disk with an actuator, a read/write head on a mechanical arm. The hard drive reads/writes data magnetically. This magnetic property can lead to the breakdown of magnetic behavior, but in SSD, there is no moving part to break up. The SSD has two key components namely flash controller and NAND flash memory.

4. Online cloud storage

Online cloud storage is used by cloud computing environment where data/information is stored in a remote location. Cloud storage has data centers that helps the users to store and access data over the internet from anywhere in the world. Many cloud-based services are provided to the users, such as Apple (iCloud), Amazon (Amazon Web Services), Google Cloud, Dropbox, etc. The application is deployed in multiple servers connected to the internet and the computations are distributed to several nodes that can run in parallel. Cloud services include online data storage, infrastructure and applications. It combines hardware and software-based computing resources to provide network services. By using the cloud, users can access files, documents, and applications on almost any device. Instagram, Facebook, Gmail, and other applications are deployed in a cloud environment.

Cloud storage

Characteristics of Storage Types

The 6 major characteristics of storage devices that are to be considered are listed below:


It refers to how quickly a computer can read and write data to and from the device. The SSD is faster than RAM. And magnetic tape is slowest of all storage devices.


Storage costs can be calculated in a variety of ways. It can be calculated as the cost per MB or as the total cost of the device. Although the cost per MB may be higher in some cases, the capacity requirements are smaller, making the cost per device more affordable - for example, CDs and DVDs.

In terms of dollars per gigabyte, SSDs are more expensive than hard discs. A 1TB 2.5-inch internal hard drive costs between $40 and $60, whereas the cost of cheapest SSDs of the same size and form factor is about $100.


The amount of disc space provided by one or more storage devices is referred to as storage capacity. It quantifies the amount of data that a computer system can hold. For example: The storage capacity of a network server with five 1TB discs is 5 terabytes.

The magnetic tape can store up to about 5TB. CDs can store 650MB data and DVDs can store 4.7GB to 17GB.


Durability refers to the protection of data over time that means the data is not corrupted by bit rot, deterioration or by other means. It focusses on data redundancy rather than physical redundancy to ensure that data is never lost or corrupted.

The M-Disc is a claimed "permanent storage solution" optical media storage disc.


If the device can be detached and can be carried separately, then it is said to be portable. The example of portable devices are smartphones, laptop, tablet, notebook, ipods and so forth.

The magnetic tape itself is thin and narrow and it is portable. Floppy disks are available in sizes 5.5-inches, and 8-inches respectively and the popular size is 3.5-inches. It is also a portable whereas internally used hard drives in a computer system are not portable.


Reliability refers to whether a device can be relied on to perform consistently. Cloud services are reliable since the data and application are replicated in several nodes and therefore, they are available always even when one node fails. SSDs are highly reliable storage devices since it provides consistent performance over a longer period of time.

Difference between Magnetic disk and Optical disk

S. NoOptical diskMagnetic disk
1It sample rate is very highIt sample rate is low.
2In this media tape used is single removable diskMedia tape used is Multiple fixed disk
3In this the data is sequentially accessed.In this the data is randomly accessed.
4Mass replication is possibleOnly one disk used at the time
5Excellent signal to noise ratioIntermediate signal to noise ratio
Difference between optical disk and magnetic disk

Difference between Hard disk and Floppy disk

S.No.Hard diskFloppy disk
1It's dependable.It isn't as dependable as a hard drive.
2It is not portable easilyIt is easily portable
3It is widely used now-a-daysIt is very less used almost not used.
4It has better security from virusesIt is susceptible to viruses.
5In this The data can not be damaged and corruptedThe data can be damage or corrupted.
Difference between hard disk and floppy disk

Common Mistakes

Students may get confused regarding disk and drive. In many cases, both are even used interchangeably. But, there is a difference between them. A disk is a physical storage device, whereas a drive is a file system stored on a disk or part of a disk. All drives store files and programs that are used by the computers.

Context and Applications

This topic is significant in the professional exams for both graduate and postgraduate courses, especially for:

  • Bachelors in Computer Science
  • Bachelors in Information Technology
  • Masters in Computer Science
  • Storage management
  • RAID levels
  • Memory hierarchy
  • Cloud storage

Practice Problems

Q1- Which device has the smallest storage capacity?

  1. Floppy disk
  2. SSD
  3. Hard disk drive
  4. USB

Correct Answer: 1. Floppy disk

Explanation- Floppy disks are 3.5 inches in size with a standard capacity of 1.44 MB.

Q2- Which is an example of optical storage device?

  1. CD-R
  2. DVD
  3. CD-ROM
  4. All of these

Correct Answer: 4. All of these

Explanation- Optical storage devices use lasers and lights to store the information/data, which means the data is read and written with a laser. CD-R, DVD, CD-ROM are the example of optical storage device.

Q3- What is the full form of RAM-

  1. Random Access Memory
  2. Read Access Memory
  3. Random Access Machine
  4. None

Correct Answer: 1. Random Access Memory.

Explanation- The full form of RAM is a Random Access Memory. It is a non volatile memory. The nature of RAM memory makes it unsuitable for long-term storage.

Q4- Secondary storage memory is essentially:

  1. impact memory
  2. non-volatile memory
  3. backup memory
  4. volatile memory

Correct Answer: 2. non-volatile memory

Explanation- The secondary storage memory is known as Read Only Memory. The Central Processing Unit has direct access to ROM. However, the data and instructions contained in ROM are preserved even when the computer is turned off. So this memory is known as non-volatile memory.

Q5- When power is switched off, the storage will lose its data. Such type of memory is:

  1. non-volatile storage
  2. backup storage
  3. impact memory
  4. volatile memory

Correct Answer: volatile memory

Explanation- When the system's power is switched off, the contents in volatile memory are deleted. RAM (Random Access Memory) is an example of volatile memory.

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