CDs

Compact discs (CDs) are optical storage media developed in the 1980s by Philips and Sony. They were designed for audio but later supported data formats such as CD-ROM. The standard CD is a 120 mm disc that can hold about 700 MB of data or roughly 80 minutes of audio. A smaller 8 cm miniCD exists with substantially less capacity.

CDs are read by a laser and store information as microscopic pits and lands arranged in a continuous spiral track. Data integrity is maintained by error-correction codes, notably CIRC, which allow recovery from minor scratches or defects. The format originally used a constant linear velocity for audio and later varied speeds for data discs, enabling different playback and access characteristics.

Common formats include audio CDs for music, CD-ROMs for data, CD-R and CD-RW for writable formats, and CD-G for graphics accompanying audio. Disc production can be mass-replicated for distribution or created by consumers on blank media with appropriate burners. Writeable variants use different recording dyes or phase-change materials and have distinct lifecycle considerations, such as longevity and rewrite limits.

Today, CDs have declined in mainstream use due to streaming, downloads, and durable flash storage, but they remain in circulation for music distribution, software delivery, and archival storage in some settings. They also retain niche value for collectors and enthusiasts who emphasize hardware compatibility and tangible media.

In finance, CDs also refer to certificates of deposit, a type of bank time deposit with fixed terms and interest. Terms typically range from weeks to years and are often insured by government programs (for example, the FDIC in the United States) up to applicable limits; early withdrawal penalties may apply.