Secondary Memory

Table of Contents


External storage or auxiliary storage, commonly known as secondary memory, plays a vital role in the field of computing. It acts as a storage space for data and information that can be accessed and retrieved over the long term. Unlike primary memory (RAM), which offers fast but temporary storage, secondary memory provides a more permanent and larger storage capacity. This makes it an essential component of any computer system, enabling users to store, manage and preserve their data beyond immediate processing requirements.
Various forms of secondary memory devices are available, including hard disk drives (HDDs), solid state drives (SSDs), optical discs (such as CDs and DVDs), USB flash drives and cloud based storage solutions. Each of these devices has its own unique characteristics, advantages and limitations that make them suitable for different purposes.

What is memory

Computer memory, in the realm of computing and information technology, plays a crucial role as a fundamental component of a computer system. It enables the storage, access and manipulation of data and instructions. There are different categories of computer memory, including primary memory and secondary memory.

Primary Memory

Primary memory is the main memory of a computer system. It consists of semiconductors and is primarily used to temporarily store data or information that the computer is currently working on. However, this data or information is lost when the system is powered off. Primary memory can be further divided into two types; 
  1. Read Only Memory (ROM) 
  2. Random Access Memory (RAM).





Secondary Memory

secondary memory serves as an additional storage option with larger capacity compared to primary memory. Unlike primary memory, secondary memory retains data and programs even when the computer is turned off. It acts as auxiliary storage for storing programs and data.
Secondary or external storage devices are distinct from primary memory because they are not directly accessible through the CPU and are non volatile. Moreover, secondary memory offers a significantly larger storage capacity and is more cost effective compared to primary memory.

Use of Secondary Unit

The main purpose of secondary memory in computing is to provide long term storage for data, programs and files that need to be saved beyond the immediate session or power cycle of a computer. Secondary memory serves several important functions;
  1. Storing Data; It allows users to store their data, applications and operating systems so they can be accessed even when the computer is turned off or restarted. This ensures that information remains available over time.
  1. Backup and Recovery; Secondary memory plays a crucial role in creating backups of important data. In case of any data loss, it provides a way to restore files and system configurations, ensuring the integrity of data and uninterrupted business operations.
  1. Large scale Storage; Secondary memory devices typically offer larger storage capacities compared to primary memory (RAM), making them ideal for storing large amounts of data such as multimedia files, databases and archives.
  1. Data Transfer and Sharing; External storage devices like USB flash drives and external hard drives facilitate easy transfer of data between computers. They enable users to conveniently share files and carry their data with them.
  1. Installation of Applications and Operating Systems; Operating systems and software applications are usually installed from secondary memory onto primary memory (RAM) for execution purposes. This enables computers to run various programs efficiently.
Reliability and Durability; Secondary storage is designed to retain data even when the power is turned off, making it reliable for long periods of time. This ensures that important data remains intact over extended durations.
Data Archiving; It offers a way to store and preserve historical or infrequently used data, which helps free up primary storage and enhances system performance.

Type of Secondary Memory

Type Of Secondary Memory
Type Of Secondary Memory

Fixed storage

In secondary memory, fixed storage refers to an internal media device utilized for storing data in a computer system. Fixed storage is commonly known as fixed disk drives or hard drives. Typically, computer system data is stored in a built in fixed storage device. However, it’s important to note that fixed storage devices can be removed from the computer system for repair, upgrades, maintenance, etc., with the assistance of an expert or engineer.
Types of fixed storage;
The following are different types of fixed storage;
  1. Internal flash memory (less common)
  2. SSD (solid state disk)
  3. Hard disk drives (HDD)

Removable storage

In secondary memory, removable storage refers to an external media device used for storing data in a computer system. Removable storage is generally referred to as disk drives or external drives. It is a portable storage device that can be inserted into or removed from the computer according to our needs even while the computer is running. These removable devices allow easy transfer of data from one computer to another.
Moreover, removable storage devices offer the rapid data transfer speeds that are typically associated with storage area networks (SANs).
There are various types of removable storage options available, such as optical discs (CDs, DVDs, Blu ray discs, etc.), memory cards, floppy disks, magnetic tapes, disk packs, paper storage (punched tapes, punched cards, etc.) and other secondary memory devices.
  1. The floppy disk, which comes in two sizes (3.5 inches with a storage capacity of 1.44 MB and 5.25 inches with a storage capacity of 1.2 MB), is a magnetic disc enclosed in a square plastic case. It serves the purpose of storing and transferring data between devices. However, floppy disks have become obsolete now and have been replaced by CDs, DVDs and flash drives since then.
  1. The compact disc (CD) is a widely used secondary storage device that has tracks and sectors on its circular polycarbonate plastic surface. It can store up to 700 MB of data. Sometimes referred to as CD ROM (Compact Disc Read Only Memory), computers can read data from it but cannot write new data onto it without specialized equipment called CD ROM drives or burners. There are two types of CDs; CD R (compact disc recordable)Once the information has been stored on it, it cannot be removed completely; however, it can be accessed and retrieved multiple times. CD RW (compact disc rewritable) is a unique form of CD that allows for data to be erased and rewritten whenever necessary. It is also known as an erasable CD.
A Digital Versatile Disc, commonly known as a DVD, resembles a CD in appearance but has a higher storage capacity. It can store up to 4.7 GB of data. To use a DVD on a computer, you will need a DVD ROM drive. DVDs are often used to store video files such as movies or recordings, which can be played on a DVD player.
There are three types of DVDs;
  1. DVD ROM (Digital Versatile Disc Readonly); In this type, the manufacturer writes the data onto the disc and users can only read the content; they cannot write new data onto it. For instance, movie DVDs come pre written by the manufacturer, allowing us to watch movies but not modify their content.
  1. DVD R (Digital Versatile Disc Recordable); With this type of DVD, users can write data onto it once. Once the information is written onto it, it cannot be erased; it can only be read.
  1. DVD RW (Digital Versatile Disc Rewritable and Erasable); This special type of DVD allows users to erase and rewrite data multiple times as needed. It is also referred to as an erasable DVD.
  2. A Blu ray disc bears a resemblance to a CD or DVD, but it has the capacity to hold up to 25 GB of data or information. To utilize a Blu ray disc, you will require a Blu ray reader.


From traditional high capacity hard disk drives to lightning fast solid state drives and the convenience of cloud storage solutions, there is a wide variety of secondary memory options available to meet the diverse needs of individuals and businesses alike. These options ensure that valuable information ranging from personal photos and documents to critical business data remains secure and easily accessible.
In summary, secondary memory plays a crucial role in contemporary computing, serving as an essential and long lasting storage option for our continually expanding digital requirements. Its capacity to hold extensive quantities of data, preserve it for extended durations and allow easy access is of utmost importance in today’s digital era.
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