Types Of Computer Hardware – Optical Storage Devices and Media

Optical disc

The optical storage system began with optical discs popularly known as Compact Discs (CD) which were developed in 1990 based on optical laser technology. These were later superseded by the Digital Versatile Disc (DVD), and the Blu-ray Disc (BD).

Optical discs are flat, round, portable strong plastic called polycarbonate. These discs are usually 120mm or 4.75 inches in diameter and less than one-twentieth of an inch thick. There are also smaller 80mm or approximately 3 inch mini CDs and mini DVDs.

Keep reading this post to learn something about optical disc drive and optical disc.

What is Optical Disc Drive and Optical Discs?

Optical Disc Drive

The Optical Disc Drive is used to read or retrieve information on the disc by focusing a laser beam on the surface of the spinning disc. Some areas of the disc which are flat reflect the laser light into a sensor, and other areas which are depressions or hollows scatter the light.

The spot that reflects the laser light into the sensor is interpreted as a land bit=1, and the absence of a reflection is interpreted as a pit bit=0. The drive is also used to write or store data on the disc in a long spiral track. The process of recording or writing data onto an optical disc is called burning.

Optical Disc

Optical discs are commonly used for storing high-capacity music and video files, multimedia presentations, and for backup of information. Optical discs are also the standard today for software delivery. Several types of optical discs can be identified based their different features. These include Read-Only Optical Discs, Recordable-Discs Optical Discs, and Rewritable Optical Discs.

Read-Only Optical Discs


A distinguishing feature of Read-Only Optical Discs is that data stored on the disc cannot be erased, changed, or added to by the user. These discs come in different qualities and storage capacities. The following ca be identified: CD-ROM, DVD-ROM, and BD-ROM.

These ROM discs usually come prerecorded with commercial products such as music, movies, software programs, clipart, and other types of graphics by companies.

  • CD-ROM – CD-ROM (Compact Disc Read-Only Memory) is an optical disc with a typical storage capacity of 650 MB or 700 MB that can only be read from but not written to, or data on it erased or changed by the user. This is because pits molded into the surface of the disc during production are permanent. CD-ROM discs are designed to be read by CD-ROM drives.
  • DVD-ROM – DVD-ROM (Digital Versatile Disc Read-Only Memory) also known as Digital Video Disc Read-Only Memory. It is also an optical disc with a typical storage capacity of 4.7 GB (Single layer disc) or 8.5 GB (Double or Dual layer disc). These discs can only be read from but not written to by the user because pits were molded permanently into the surface of the disc. DVD-ROM discs are designed to be read by DVD-ROM drives which also have the advantage of reading information stored on CD-ROMs.
  • BD-ROM – BD-ROM (Blu-ray Disc Read-Only Memory) is a type of high capacity optical disc with a storage capacity of 15 GB (Single layer disc) or 30 GB (Double layer disc) that is designed for storing high-definition information such as graphics and movies. The data on a BD-ROM can also not be erased because the pits were molded permanently into the surface of the disc when the disc was being produced. Blu-ray discs are produced to be read by Blu-ray disc drives.

Recordable Optical Discs


A unique feature of Recordable Optical Discs is that it can be written to by a user but information on it cannot be erased and reused by anybody. These discs also come in different qualities and storage capacities which include: CD-R (Compact Disc-Recordable), DVD-R/DVD+R (Digital Versatile Disc-Recordable) and BD-R (Blu-ray Disc-Recordable).

  • A CD-R has a storage capacity of 650 MB or 700 MB and a user can record or write information on a recordable disc. However, information on it cannot be erased, changed or added to, once it is written and the disc cannot be reused. CD-R discs are made to be used by CD-Recordable drives to record information.
  • DVD-R/DVD+R discs have the same storage capacity as their DVD-ROM counterpart and also allows the user to record or write information on the recordable disc. However, nobody can erase, change or add any information on it once it is written and the disc cannot be reused. It is designed to be used by DVD-Recordable drives to record information.
  • BD-R discs typically have a storage capacity of 25 GB (Single layer disc) or 50 GB (Double layer disc). BD-R discs can also only be written to and their contents can neither be erased, changed nor added to, and it cannot be reused as well. It is used by BD-R drives to record information on them.

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