Between the ubiquity of VHS tapes and the convenience of digital streaming, not to mention many forgotten nostalgic formats like LaserDisc, DVDs reigned supreme on the home entertainment scene. With affordability and high resilience, DVDs could store digital information on their internal reflective layers and, depending on the precise DVD model, even rewrite their information for convenient storage purposes. Whether you’re watching movies or sharing data with friends, DVDs made it all easier in the early 2000s, and with proper care, DVD and Blu-Ray collections can still last a long time today.
DVDs are similar to digital compact discs (CDs), with roughly the same size, thickness, and materials. Rather than a radical difference in materials or manufacturing, DVDs differ from CDs and other similar formats by their use of multiple layers of data storage, made of polycarbonate plastic injected just below the surface of the disc. These layers can be read and analyzed by a red laser from a DVD player or PC disc drive, allowing you to access and play the files stored on them. DVDs paved the way for Blu-Ray discs after them, with ever-increasing data storage capacities.
Data is stored on multiple writable layers
Both sides of the DVD are made of polycarbonate (PC), but the bottom side is transparent, while the top side usually has a label. Beneath the base layer of the DVD surface is a second reflective layer made of metals like aluminum and gold. That’s why when you expose the bottom of a DVD to a light, it glows in a distinctive rainbow of colors.
Below a DVD is a spiral data track, rotating outward from the center. Along this spiral track are a multitude of microscopic bumps, also called pits. When you place a DVD in a DVD player, the player emits red laser light onto the underside of the disc, penetrating the PC layer and reaching the recesses of the reflective layer. Next to the laser transmitter is a sensor that determines when and at what intensity the light is reflected. As the disc spins, the sensor analyzes the presence or absence of dips as binary code, with the entire sequence stored in the data track gradually adding up to form the files stored on the DVD.
The indentations of a read-only DVD are printed during its manufacturing process and cannot be changed afterwards. However, there are also rewritable DVDs, which use special phase change material. When a laser is shone on this material, it changes state between amorphous and crystalline, creating an effect similar to the pitted discs that a DVD player can analyze. Since the hardware state can always be changed, you can always modify the content present on the DVD.
Other storage media like Blu-Ray store data differently
Read-only CDs and DVDs are made the same way and with similar materials, and they store and read data the same way, generally speaking. Both use microscopic pinholes in a reflective layer and both are read by a laser transmitter and sensor. The difference between them is that the dips on a DVD are exponentially smaller, so more of them can be packed together along its surface.
This results in a storage medium with much more storage space. Additionally, a DVD player’s laser has a narrower focus, allowing it to read smaller, tighter pits. The laser on a CD player is too wide to properly scan the dips in a DVD, so nothing would happen if you tried to play a DVD on one. Blu-Ray discs also use many of the same manufacturing principles and materials as DVDs, but they take their technology even further.
Although they only use a single layer compared to the two-layer approach of a DVD, Blu-Rays contain even more compact data tracks with even smaller and more voids. A Blu-Ray player uses blue-violet laser light with an even narrower focus, with the added benefit of an additional lens placed closer to the playback mechanism. This all adds up to even greater storage capacity, which also means greater fidelity for video files. These types of physical disks remain a great way to store data, which may partly explain why Gen Z is more interested in physical media.
