A CD, short for , is an optical storage device that was widely used for audio playback and data storage in the late 20th century and early 21st century. It was one of the primary methods of distributing , software, and other digital content. A CD consists of a polycarbonate disc that is coated with a thin layer of or other reflective material. The disc is divided into spiral tracks, starting from the center and extending outwards. These tracks are further divided into and lands, which represent the binary data stored on the disc. To read the data from a CD, a laser beam is focused onto the disc surface.
The reflective layer reflects the laser light differently when it encounters pits or lands. This light variation is detected by a sensor, which converts it into electrical signals. CDs have several advantages, including relatively large storage capacity, ability to be played on various devices, durability, and cheap distribution. However, compared to modern storage devices, CDs have a relatively data transfer rate and can be damaged by sunlight, extreme temperatures, and improper handling. Many modern PCs, especially , no longer have a CD drive, making them somewhat obsolete.
DVDs, or digital versatile discs, can store larger amounts of compared to CDs and are commonly used for movies and software. A standard single-layer DVD can hold about gigabytes of data, while a dual-layer DVD can store up to 8.5 GB. Although DVDs are portable and easy to distribute, they can get scratched or damaged easily, and their popularity has declined with the rise of formats such as streaming. Blu-ray is another type of optical disc that can store large amounts of , including high-definition videos, games, and multimedia content, using a blue-violet laser instead of the red laser used in DVDs.
Keywords
photodiode | data | laptops | aluminum | 4.7 | compact disc | music | slower | digital | data | pits |
