Optical storage discs like CDs and DVDs rely on laser technology to read and write data encoded into physical patterns. A standard Compact Disc (CD) maxes out at 700 MB of data, while a standard Digital Versatile Disc (DVD) holds 4.7 GB.
The technical specifications, physical track structures, and variances in storage capacities explain why these formats look nearly identical but perform differently. Understanding the Technical Specifications
Optical discs store information along a single, continuous spiral track that runs from the inside of the disc out to the edge. Data is written by a laser that burns tiny physical indentations called pits into a reflective layer, leaving flat gaps called lands. A drive reads this data by bouncing a laser off the surface; the transitions between pits and lands alter the reflection, which the system translates into binary 1s and 0s.
A direct breakdown of the specifications for each format includes: Technical Spec Compact Disc (CD) Digital Versatile Disc (DVD) Laser Wavelength 780 nm (Infrared) 650 nm (Red) Numerical Aperture Track Pitch 1.6 micrometers (μm) 0.74 micrometers (μm) Minimum Pit Length 0.83 micrometers (μm) 0.40 micrometers (μm) Standard Dimensions 120 mm diameter, 1.2 mm thickness 120 mm diameter, 1.2 mm thickness Why DVDs Store More Than CDs
Despite sharing identical physical dimensions, a standard DVD holds roughly seven times more data than a standard CD. According to the Compact Disc Wikipedia Page, a CD utilizes a wider infrared laser wavelength.
Conversely, a DVD uses a narrower red laser and a higher numerical aperture lens to tightly focus the beam. This allows the pits to be etched much smaller and the spiral tracks to be packed closer together, drastically multiplying the available data density. Storage Capacities by Disc Variant
The actual volume of data a disc can hold varies according to its physical construction and the layers of data it contains. 1. Compact Disc (CD) Variants
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