In addition, many DVD players can also play CD-R/RWs, MP3-CDs and JPEG PhotoCDs. Also, some DVD players can also play SACD (Super Audio CDs) and DVD-Audio Discs.
If a DVD Player Can Play CDs, Then Which is Better For Playing CDs - A DVD Player or a CD-only Player?
CDs and DVDs, although sharing some basic similarities, such as the size of the discs, and the the fact that they are both digitally encoded formats - they are very different. CDs have different focusing requirements than DVDs, so, in order for a DVD player to play CDs they need one of two things: A laser that has the ability change its focusing accurately based on DVD or CD detection or, more commonly, a DVD player will have two lasers, one for reading DVDs and one for reading CDs. This is often referred to a Twin-Laser Assembly as is usually listed in the spec sheet for DVD players that have them.
The reason that DVD players can also play CDs is not so much technical, but is a conscious marketing strategy. When DVD was first introduced to the market in 1996-1997, it was decided that one of the best ways to increase sales of DVD players and make them more appealing to consumers was to also include the ability for DVD players to also be able to play CDs. As a result, the DVD player actually became two units in one, a DVD player and a CD player. Although some audio processing circuitry is shared, the basic requirements of both CD and DVD compatibility are accommodated separately within the same chassis.
Now, as to whether ALL DVD players are better CD players, not all are. You have to compare them unit-by-unit. However, a great many of them are, especially DVD/SACD/DVD-Audio Universal Players, due their higher-end audio processing. Also, as a result of the popularity of DVD and CD, it is becoming harder to find CD-only players. In fact, most CD-only players available these days are either the Jukebox type that hold 50 or more CDs, or very high-end single tray units.