What is a CD

Table of Contents


A compact disc is a portable storage device that can be used to record, store and play back digital audio, video and other data.
The standard size of a compact disc is 4.7 inches or 120 millimeters (mm) in diameter. It has a thickness of 1.2 mm and weighs between 15 grams and 20 grams. In terms of capacity, it can hold up to 80 minutes of audio or approximately 650 megabytes (MB) to 700 MB of data.

 What is a CD?

A CD utilizes a semiconductor laser with a wavelength of 780 nanometers that focuses on a single track on the disc. As the disc spins, the laser measures variations in how light reflects off the polycarbonate layer at the bottom of the disc, converting it into sound.
Compact discs are delicate and prone to scratches; while they can be repaired, their readability may be affected.

History of compact discs

The origins of compact discs trace back to James Russell, an American inventor who envisioned an alternative to vinyl albums for storing and playing audio recordings. In 1966, he filed a patent for a product that combined laser technology with digital recording and optical discs. In subsequent years, Philips Electronics and Sony Corp obtained licenses for this technology.
In terms of commercial availability, the first ever compact disc was released in 1982. It featured recordings of Chopin waltzes performed by pianist Claudio Arrau.
Before that, test recordings were finished in the year 1979. In 1981, the BBC showcased a CD playing the album “Living Eyes” by the Bee Gees.
A commercially available compact disc player, known as the CDP 101, was introduced in 1982 and people around the world started using this format.

Compact disc formats

Different compact disc formats emerged with the advent of personal computers and other commercial technologies. Sony and Philips, in their Rainbow Books, introduced specifications for these CD versions, which were named after the colorful book bindings. The Red Book defined the standards for a standard CD.
There are several variations of compact discs, including;
  1. CD Read Only Memory (CD ROM); Launched in 1985, CD ROMs not only allowed audio playback but also enabled optical data storage. These discs can be read by any computer equipped with a CD ROM drive. The Yellow Book establishes the standards for CD ROMs.
  1. CD Interactive (CD i); Introduced in 1993, CD i discs could be played on regular CD players but were initially incompatible with CD ROM drives. However, later modifications made them compatible with both types of devices. The Green Book provides specifications for the CD i format.
  1. CD Rewritable (CD RW); Utilizing a metallic alloy that reflected light differently from regular CDs, these discs faced compatibility issues with early models of CD players due to changes in reflectivity. The Orange Book defines the standards for creating and using CD RW discs.
  1. CD Recordable; This variation is not further described or specified.
The CD R is a type of compact disc that can be written to one time and read multiple times. It adheres to the Orange Book, just like the CD RW. However, unlike the CD RW, the CD R can be played on CD players that were released before its own introduction.
  1. CD ROM eXtended Architecture, also known as CD ROM XA, is an extension of the standard CD ROM format that allows simultaneous access to audio, video and computer data. It follows the Yellow Book standard and was designed as a link between CD ROM and CD i.
  1. The photo CD, developed by Kodak, was specifically designed to store digital photographs that could be easily accessed and edited on a computer. It was introduced in 1992 and initially had the capacity to hold up to 100 high quality images. This format followed the Beige Book standard.

The future of compact discs

In 1993, the video CD (VCD) was created according to the White Book standard. Although VCDs were intended to offer comparable quality to VHS recordings, they have lower resolution compared to modern digital video disks (DVDs).
The usage of CDs has steadily declined over time, especially during the early 2010s. In the music industry, digital formats have taken over CDs due to the rise of streaming audio and digital downloads. While compact disc sales were more profitable for music industry professionals, fewer consumers now rely on physical mediums due to convenience and cost effectiveness.
During the era when compact discs gained popularity, personal computers could only store around 10 MB of data. As a result, many people turned towards CDs as a storage solution. However, this is no longer true today.
With the constant influx of higher capacity hard drives and various online storage alternatives, compact discs and tape cartridges are no longer the preferred choice for many consumers.
To potentially replace compact discs, Philips, Sony and Toshiba collaborated in developing the DVD format. DVDs have identical dimensions to CDs but possess a significantly larger storage capacity of 4.7 gigabytes (GB).

Different Types of Compact Discs

There are three main types of compact discs available;
  1. CD R; The full form of CD R is Compact Disc. Recordable. This type of disc can be written to only once and cannot be erased.
  1. CD ROM; CD ROM stands for Compact Disc. Read Only Memory. These discs can only be read once, after which they function as a ROM and cannot be updated.
  1. CD RW; The full form of CD RW is Compact Disc. ReWritable. This type of disc can be written to multiple times and can also be erased, similar to a pen drive.

How a Compact Disc Works

Compact discs, commonly referred to as CDs, typically have a diameter of 12 cm or 4.5 inches and consist of four distinct layers;
  1. Top Layer
  2. Lacquer Layer
  3. Reflective Layer
  4. Polycarbonate Disc Layer

Advantages of Compact Discs

Compact discs offer several advantages;
  1. Portability; CDs are more compact and lightweight, making them easier to store and carry around.
  2. Reliability; In the past, entire software applications could fit on a single CD, making it highly reliable for the software industry.
  3. Versatility; CDs have proven adaptable for various purposes beyond storing digital audio due to their higher capacity.
CDs gained popularity as a means of distributing home movies, software packages and other digital content.

Drawbacks of Compact Disks

Limited Storage Capacity; Although CDs offered more storage capacity than previous mediums, newer options such as hard drives and DVDs now offer greater capacity. As a result, CDs are not commonly used anymore.
Outdated Technology; The limitations of compact discs can be attributed to their older technology for reading and writing data, which relies on a 780nm wavelength.
Designed by Kodak, the photo CD was created for the express purpose of storing photographs in a digital format that could be accessed and edited on a computer. It launched in 1992 and was originally designed to hold 100 high-quality images. It followed the Beige Book standard.
Video CD. The video CD, or VCD, was created in 1993 and followed the White Book standard. VCD quality was intended to have comparable quality to VHS recordings, but has a much lower resolution than a modern digital video disk (DVD).
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