What is CD (Compact Disc) and How It Works?

According to the release year of the album, they put physical CDs on the shelf in turn, which has an unspeakable sense of satisfaction. There is also a relatively large group of fans, in order to support their idols to buy their idol's physical CDs. Some record companies have also found a new position for them -- a "giveaway" bundled with concert tickets.

Despite streaming media has become the main way for most people to listen to songs, CD came out in 1982 and is still the standard storage format for commercial recording. Let's see what a CD is and how does CD work?

Part 1. What is CD (Compact Disc)?

CD stands for small laser disk, a general term for all CD media formats. On October 1, 1982, Sony released the world's first commercial CD player, opening the digital audio revolution. It heralds the era of a new audio medium that promises to deliver a clear music experience to a generation of consumers accustomed to the hissing sound of vinyl records. Because of the great success of CD, today the use of this media has been expanded to data storage, with the purpose of data archiving and transmission.

Before the Invention of CD

Compared with various traditional data storage media such as floppy disk and audio tape, CD is the most suitable media for storing large amount of data. It may be any form or combination of computer files, audio data, photo image files, software applications and video data. The advantages of CD include durability, convenience, and limited cost.

Before the invention of CD, most of the sources of music were LP records with a diameter of 30cm, radios and recorders. In earlier time, there even had no digital sound at all. Therefore, CD is the greatest invention since transistor.

The Development of CD

Originally, it was only designed for the consumption of home appliances and the market of music records. It was not thought that CD could be used on computers in the future. CD technology was later used to store data, known as CD-ROM. By 2007, CD-ROM had become one of the most widely used storage media in the PC industry. CD and its derivative formats have achieved great success. In 2004, the total sales volume of Audio CD, CD-ROM, CD-R and CD-RW reached 30 billion.

Since CD appeared in the market, the 30 cm diameter analog LP Record began to fade. In the future, all similar CD products, including DVD and Blu ray discs, are derived from this.

Part 2. How Many Types of CD Do You Know?

Initially, discs could only be read, but the new technology allows users to use discs for recording. The electronic industry soon discovered the potential of CD, and understood that this product can not only be used as a carrier for music. Therefore, electronic companies began to use it in many fields, such as video and photo storage.

CD Variants Include:

CD-Read-Only Memory: CD-ROM is the most common kind of CD.This kind of CD-ROM can only write data once, and the data be stored permanently. When it is used, the information will be read out through the CD-ROM drive. The music of CD ROMs can be played by CD players, and computer data can only be processed by computers.

CD-Recordable: CD-R is generally used to record to the customer or backup files, and cannot be deleted after the completion of cutting.

CD-ReWritable: CD-RW has a reflection layer, which can be used many times, with a limit of about 1000 times. Although it can not be used as a hard disk, it is also good for backup.

Photo CD: Photo CD is designed to store photos in a digital format that can be accessed and edited on a computer. 

Video CD: VCD was created in 1993. The quality of VCD is equal to that of VHS record, but its resolution is much lower than that of modern digital video disk (DVD).

The common CD-ROM is a single-sided disk, which is very thin. It is only 1.2mm thick, but it can contain a lot of content. The reason for not making a double-sided disk is not that it cannot be made technically, but that the cost of making a double-sided disk is higher than the sum of the costs of making two single-sided disks. The reason why it is made into a single disk can be explained from the CD data storage and how it works.

Part 3. How Does CD Work?

Data Storage

CD-ROM is mainly divided into five layers and the polycarbonate disc layer has the data encoded by using lands and pits.

The polycarbonate disc layer is the place where the information is recorded when burning. Its main working principle is to smear special organic dye on the substrate for the laser to record information. Because of the different reflectivity before and after burning, when the signals of different lengths are read by laser, 0 and 1 signals are formed by the change of reflectivity, so as to read information.

The laser beam must pass through the transparent substrate to reach the pit and read out the data. Therefore, any contamination on the surface of the side where the data is stored in the disk will affect the readout performance of the data. As a result, one side of the CD-ROM disk is dedicated to printing trademarks, while the other side is used to store data.

How CD Retrieve data?

Data is stored in tiny pits, and is read by the optical drive using a reflected laser. The laser light transforms the two states into Land and Pit on the disc. Similarly, the zeros and ones generated by Land and pits are read by optical drives and then analyzed by decoders to form the data we want to see or hear.

No matter it is CD-ROM or CD-ReWritable, the principle of the computer is to read "0" and "1" recorded on the CD through the media, because the computer can only read 0 and 1. Computers are actually made up of digital circuits, in which 0 and 1 represent two different states. So, the information recorded on the CD is actually a lot of "0" and "1".

A Brief Summary

In the heyday of CD, its value is not only reflected in the aspects of information storage media, but also a powerful data transmission mode. For decades, CD was the most effective way for consumers to bring a large amount of data back home quickly from a certain place, far faster than downloading 650mb of music through any original network available at that time. At present, CD is still the most popular physical media for data storage, and it will be the same for a long time in the future.