Difference between CD and DVD.

Why should we remember about optical media in the era of flash and cloud services? Isn't it time to free up space in museums next to magnetic cassettes, vinyl records and 1.4 ”floppy disks? But licensed high-quality media content in offline trade, software, instructions and booklets accompanying components and electronics are distributed on disks. Let's see how CDs differ from DVDs before they become history.

Contents
  1. Comparison
  2. Table

CD (Compact Disk) is an optical disk intended for storing digital information, the recording and reading of which is carried out by a laser installation. Distributed standard CDs with a capacity of up to 700 MB.

DVD - an optical disc with increased capacity compared to CD (it can have a volume of 4.7 GB, 8.5 GB, 9.4 GB, 17 GB).

Today, for most users of computer systems, it is in capacity that CDs differ from DVDs: the former stores small files, including audio, the latter - video, images of operating systems and software packages. However, the past tense is more appropriate: many are already accustomed to working with flash drives and external hard drives.

This is true for the process of exchanging information between systems. But commercially produced content on optical media is played in various media players, including hi-end-class ones. And, of course, game consoles cannot do without discs.

Comparison

As we already know, an ordinary CD contains 700 MB of data (much less often there are disks with a capacity of 650, 800, 900 MB). DVD classification in this respect is more diverse: the most common DVD-5 with a capacity of 4.7 GB, DVD-9 (8.5 GB), DVD-10 (9.4 GB), rare DVD-18 (17 GB), HD DVD (up to 30 GB). With all this, the dimensions, materials and shape of the optical medium itself are absolutely the same for all types of discs: 120 mm - diameter, 1.2 mm - thickness.

Information is recorded on a plastic base covered with a layer of metal by means of a laser - depressions of different lengths are created, arranged in spiral paths. The transparent layer of varnish does not interfere with the passage of the beam, but protects the plastic from damage. When reading, the pits (pits) absorb light, and the undeformed base reflects, and these signals are interpreted by the receiving device.

The figure clearly demonstrates the difference between CD and DVD. On the first disk (standard 700 MB), the grooved tracks are located at a distance of 1.6 µm from each other, on the second there is only 0.74 µm between them; pit length 0.8 - 3.1 microns and 0.4 microns, respectively. The seal allows for more information:

CD
DVD

Laser wavelength for reading and DVD burn rate is 650nm, while CD requires 780nm. Due to this difference, it became possible to record data in two layers, as well as use both sides (increase capacity) while maintaining the dimensions. Thus, 4.7 GB is a single-layer DVD, 8.5 GB is a single-sided dual-layer, and 17 GB is a double-sided dual-layer. CDs are always single-layer and single-sided.

Modern optical drives for computer systems are usually combined, which allows them to work with any disc. Media players are much more legible. New operating systems are legally distributed only on DVD (due to the large size of the distribution), booting from CD is supported by Windows Vista (and later) and Linux systems released before 2012.

Table

CD DVD
Standard CD can hold up to 700 MB of dataStandard DVD-5 can hold up to 4.7 GB of data, there are many higher capacity options
Track spacing - 1.6 μmTrack spacing - 0.74 μm
Laser wavelength for reading and burning - 780 nmLaser wavelength for reading and burning - 650 nm
Single-layer single-sided discsCan be double-layer and double-sided
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