3 Common Types of Optical Storage Devices and their Functionality

A storage device is a computer hardware component that writes and reads information or instructions to and from the storage media

Definition of  optical storage device

Optical storage may be defined as any type of data storage that makes use of a laser to write and read data. Optical media, such as compact discs (CDs) and digital versatile discs (DVDs), are commonly used to store information (DVDs). 

An optical disc is a type of storage media that consists of a flat, round, portable disc made of metal or polycarbonate plastic. It is coated with a thin metal or plastic or other material that is highly reflective

Optically stored data has been relegated to long-term archiving and data backup due to its capacity limitations in comparison to hard disc drives (HDDs) and later solid-state flash storage. Optical storage was originally envisioned as a potential replacement for hard disc drives (HDDs) in computing systems.

Size of Optical Storage Devices

Optical discs used in computers typically are 4.75 inches in diameter and less than one-twentieth (1/20) of an inch thick

Mini-optical discs are used in mobile devices that have a diameter of 3 inches or less

Types of Operation performed on optical storage devices

A computer performs two types of operations on the optical  storage devices

Writing Operation

In a writing process, storage device records/stores information or instructions from memory to a storage medium

Reading Operation

In a reading process, storage device transfers information or instructions from storage medium into computer’s memory (for use by OS or application program) 

What are the Advantages of Optical Disk

  • A large amount of data, software, movies, and songs, etc. can be stored on a single CD
  • Some optical storage media is read-only while others are read and write
  • Spelling disk is used for magnetic media, while disc is used for optical media

An optical disc has a single spiral track that spirals from the center to outside edge

Information on the optical disc is stored in the form of microscopic pits (small holes) and lands

A binary digit ‘0’ is represented by a pit and a binary digit ‘1’ is represented by a land

Pits are tiny reflective bumps that are created with a laser beam.Lands are flat areas separating the pits. A land reflects laser light, which is read as binary digit 1

A pit absorbs or scatters light, which is read as binary digit 0

High-powered laser beam creates the pits

A lower-powered laser light reads data from the disc

Different types of optical Storage discs

  • CD
  • DVD
  • Blu-ray Discs

CD (Compact Disk)

CD stands for Compact Disc

It is an optical disc used for storing digital data

It was originally developed for sound recording but now it is widely used for storing computer data and programs

Storage Capacity of CD

Storage capacity of CDs ranges from 350 MB to 800 MB

CDs are mostly used for storing huge amount of data, application programs, operating systems, and device drivers

Types of CDs

  • Read-only (CD-ROM)
  • Recordable (CD-R)
  • Rewritable (CD-RW)

What is input and common input devices

Rewritable CD

CD-RW (CD-rewritable) is an erasable multisession optical disc User can write and overwrite data on the CD-RW disc many times. CD-RW disc is also known as an erasable CD (or CD-E)

However, the reliability of this type of optical disc tends to decrease, each time we re-write data

CD-RW drive is used to write/overwrite and read data to and from the CD-RW.This drive is advanced and more expensive than a CD-R drive.

It can write/read data on both CD-R and CD-RW discs

Today, most of the PCs have a CD-RW drive


DVD Optical Storage

DVD stands for Digital Video Disc or Digital Versatile Disc. A DVD is similar to a CD. It has the same diameter and thickness as CD and is made up of the same material.

Data is also stored just like a CD on a spiral track in the form of lands and pits (bumps) However, DVD has larger data storage capacity and higher resolution than CD.Its data storage capacity is up to 17 GB or more

DVD is specially used to store movie films. It is also used to store huge amount of data, music, and software of large size.

DVD drive or DVD player is used to read the data stored on a DVD

A DVD player can play CDs also

Types of DVDs

  • read-only (DVD-ROM)
  • recordable (DVD-R)
  •  rewritable (DVD-RW)


DVD-R (DVD recordable) is similar to CD-R.Users can write data only once but can read it many times.Data written on DVD-R cannot be erased


DVD-RW (DVD-rewritable) is similar to CD-RW. Users can write and overwrite data on DVD-RW many times.

Blu Ray Disc

Blu-ray disc (BD) is a new type of optical storage device.This storage device is reliable, faster, and has higher storage capacity than CD and DVD.

Its storage capacity is up to 1000 GB or more

Bumps (pits) on the Blu-ray disc are much smaller and very closely (tightly) packed than DVD

This increases the storage capacity of Blu-ray discs

Blu-ray discs are better storage for storing movies because they require more storage

Blu-ray drive is used to read the information on the Blu-ray disc

Some game consoles contain a Blu-ray drive



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