Computer Science 2210

Memory Storage Devices and Media


Memory Storage Devices and Media

Primary Memory

• It is accessible by the Central Processing Unit (CPU) directly.

• It is the main memory in a computer system.

• It is faster than secondary storage.

• Generally, primary memory refers to the RAM of the system.

• Examples include RAM and ROM (solid-state).

Random Access Memory (RAM):

• The RAM holds all the files and applications that are running on the system including the OS.

• It can be accessed randomly.

• It is a volatile memory that is wiped off once the computer system is powered off.

Read-Only Memory (ROM):

• It is a non-volatile memory and it contains the data even after the computer is turned off.

• It is a read-only memory and data stores in it permanently.

• It stores the programs for the boot up, BIOS (basic input/output system) and the operation of peripheral devices.

Secondary Storage

• It is a non-volatile memory that is used by the computer to have more storage space.

• Data in this memory remains as it is even when the system if powered off.

• The data in it also remain unchanged until it is deleted or modified.

• It is also known as auxiliary or external memory.

• It stores data and programs.

• Examples include Hard Disk Drive (HDD) and Solid-State Drive (SSD).

Off-line Storage

• It refers to the storage devices that need to be inserted to the computer system in order to access, edit or delete the data.

• This type of storage is generally used to transport data files and to take a backup of important data. 

• Examples include removable HDD/SDD, flash drive, CD, Blu-ray, etc.

Types of Storage Devices

1. Solid State Storage (SSS):

• It stores data electronically and does not have any moving parts.

• It is made of silicon chips.

• It uses less power and produces less heat.

• It can be found in three types i.e. drives, cards, and modules. 

• The transfer of data is much faster because of no mechanical parts.

USB Flash Drives:

• It is also known as a pen drive.

• It connects to the computer system using a USB port.

• It comes in many storage sizes and provides an easy way to transport the data.

Memory Cards:

• Memory cards are the solid-state storage that comes in different sizes like flash drives.

• However, these cards require a card reader to read its content.

• The most common use of these cards is in digital cameras to store pictures.

Solid State Hard Drives:

• These hard drives don’t have any moving mechanical parts.

• The data is handled using flash memory chips.

• It offers high reliability, uses less power and faster data access.

2. Magnetic Storage:

• It is the most common form of storage device that is a mechanical device that connects to the computer system.

• It uses magnetization patterns to store data in a magnetizable material.

• In these storages, data is accessed using one/several heads.

• The magnetic field is manipulated to store data in the magnetic storage device.

• Floppy drive is one of the examples of magnetic storage that is no longer in use in modern computers.

3.Optical Storage Devices:

• In these devices, data is stored as patterns of dots.

• Light is used to read this stored data from the device e.g. a laser beam.

• The light beam bounces off the surface of the medium to read the data.

• The light reflects differently in the case of a dot and an empty surface.

•  The process to mark the surface using the light beam is known as ‘burning’.


• It stands for Compact Disk – Read Only Memory.

• It is a non-volatile storage device therefore data cannot be modified or deleted.

• It can store up to 800 MB of data.


• It stands for Digital Versatile Disk – Read Only Memory.

• These devices can be used in the same way as CD-ROMs, but they can hold more data.


• It is a high capacity optical disk and can hold up to 50GB of data.

• The double-layer Blu-ray can hold around 100 GB of data.

• It is used in the same way as CD and DVD ROMs but can store very high-quality HD videos.

• The ‘Blu’ represents the blue light i.e. used to read the data unlike the red light used in CD and DVD ROMs.

• Blue light has a shorter wavelength allowing more data to be stored in a close orientation.

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