What is compact disc (CD)? Definition, Types and More (2024)

Compact disc is portable storage devices used for storing digital data like recording, storing, and playing video, and audio. Compact Disc can be explained as a disc-like memory device made from plastic material.

What is a CD(Compact Disk)?

CDs or Compact Disks are optically readable media. CDs are the replacement of the phonograph disc. The main material of the CD is plastic. The shape of the plastic is circular and one side of the circular plastic is coated with the reflecting metal coating, usually aluminium. Data can be stored much more densely in optic media than in magnetic media, like Hard disk. Optic media have a much longer life span. Millions of bits are burned into this coating.

CDs can store many types of data, like audio, video, games, any documents, etc. The data are scanned by a laser beam with a CD driver to visualize the data. The only thing that is less in CD is storage capacity is very less compared to HDD or DVD and the read-write speed is also very less. The storage capacity of a CD is 700 MB only.

History of Compact Disk

At first, as CD invented in the year 1960 by the American physicist James Russell. The compact disk (CD) was introduced by Philips and Sony in 1980 and released in 1982. One day he listened to music and he recognizes that the audio quality is very poor and he tried to improve the record player. But he realized that the poor quality of the music happens due to the recorder due to the contact of the needle with the recorder.

Then he thought this can be avoided by using a light to read the music without physically touching the disk. Then he started working on digital data with optic media and found a way to record media onto a photosensitive platter with tiny bits of light and dark of size 1-micron in diameter. Then he filed a patent application in 1966, and the patent was granted in 1970. After this Sony and Philips licensed with his patents for recording using optic readable media. After all this finally, in 1982 Sony released a CD player name CDP-101. This is how CDs are introduced.

How Compact Disc Works?

Compact discs, sometimes known as CDs, typically have a diameter of 12 cm, or 4.5 inches. There are four distinct layers in it.

• Top Layer
• Lacquer Layer
• Reflective Layer
• Polycarbonate Disc Layer

The top layer is used to mark the disc’s identification marks, and it may also carry printed instructions or a name identifying the contents of the device. Below the top layer, in the lacquer layer, The device is protected from exposure to atmospheric air, which can cause oxidation. The reflective layer, which is constructed of aluminium material and is located beneath the lacquer layer, is where the laser beam is pointed in order to catch a reflection, which can then be used to read the disk’s data. The data are encoded for the compact disc to function properly in the polycarbonate layer at the bottom of the disc.

A CD player or disc drive is required in order to access a compact disc. It is made up of a variety of hardware components, including a tiny laser beam and another tiny electronic light detector, within a CD player. Here, a semiconductor diode laser is used to produce the laser beam, and a photoelectric cell serves as the electronic light detector.

When the CD player or disc drive is turned on, the internal motor of the device enables the compact disc to rotate at a significant high speed, between 200 and 500 rotations per minute. This causes the internal semiconductor diode laser to be powered up and begin scanning the disc’s tracks from the centre outward. To read the data from the base layer, this is transferred through the disc. As a result, the reflection that was generated can retrieve the data from the CD and provide it to the device accessing the CD. The digital light detector can receive the reflection and read the electronic contents that are already saved into the storage unit.

Characteristics of Compact Disk

The standard diameter of a CD is 120mm and thickness is 1.2mm. The main body of the CD is made of hard plastic known as polycarbonate with a reflective metallic layer. This layer is coated with metallic acrylic plastic. This metal is aluminum. In this layer, the data are stored using the laser light which reflects the coated layer for reading and writing the data. The data is read in the form of pits, each pit is of 0.83-micrometre and the data is arranged as spiral track from the disc’s inner hole to its outer edge, because the CD is of circular shape.

The hole is in the centre of the CD, which diameter is 15mm. The area closest to the hole is known as the clamping area, no data is stored in this area because there is no metallic layer. This area is nearly equal to 26 mm to 33 mm in radius. The radius of the usable area, that is where the data can be store is of 38mm.

Types of Compact Disks

There are three types of CDs available:

• CD-R : CD-R full form is Compact Disc – Recordable. This type of compact disc can be written only once and can not erased.
• CD-ROM : CD-ROM stands for Compact Disk-Read Only Memory. This disks are read once, after read it is use as a ROM, that is cannot be updated later.
• CD-RW : CD-RW full form is Compact Disc-ReWritable. This type of compact disc can be written multiple times and can be erased also, like Pendrive.

Advantages of Compact Disk

• Portable: CDs are more compact and lightweight, they are easier to store and travel.
• Reliable: In that time, an entire software can be stored on one CD, so its very reliable for the software industries in the days.
• Multiple Applications: It is also adaptable. The higher capacity of the compact disc was exploited for uses other than storing digital audio. CDs became a popular media for distributing home films, software packages, and other digital content.
• Random Access: CD provides random data access. Users can use this random access to choose music tracks, specific files or data, or explore a menu via a user interface.
• Rewritable Formats: Another benefit of compact discs is the availability of rewritable versions such as CD-R and CD-RW.

Disadvantages of Compact Disk

• Inferior Capacity: CDs have more storage capacity than their predecessors, but subsequent storage mediums have more capacity. Storage capacity is lower than a hard drive or DVD, now a days CD is not used at all.
• Older Technology: A compact disc’s limitation stems from its older read and write mechanism technology, which is based on 780nm wavelength.
• Inferior Quality: It should be noted that audio-video files with higher audio and video quality can be stored on DVDs and Blu-ray Discs.
• Durability Issues: Magnetic tapes are less durable than CDs. However, it is still fragile because it is easily scratched if not treated carefully. When exposed to severe heat and humidity, it might deform and become unusable.
• Obsolete Medium: Another issue of CDs is that they have become obsolete as better storage methods have become available.
• It’s also worth noting that compact discs aren’t suitable for backup storage because of their limited storage capacity, susceptibility to breakage, and obsolescence. It is preferable to use hard drives or solid-state drives.

Compact Disk – FAQs

1. How much data does a CD hold?

The normal CD can contain 72 minutes of music or 650 MB of data. An 80 minute CD can hold 700 MB of data.

2. What are compact discs used for?

Compact discs are mostly used for audio and data storage. CD are mostly used for for listening to music.

3. What is size of a compact disc?

Compact discs are majorly 1.2mm(0.05 Inch) thick with a diameter of CD is 120mm(4.75 Inch).