CD stands for Compact Disc, an optical medium that can store digital data. This was the medium that was created to replace the old cassette tapes. A standard CD can hold 700MB of data, around 80minutes of CD quality audio, or up to 60minutes of video. The later standard called the Digital Versatile Disc or DVD is still an optical media much like the CD but with much greater capacities, starting at 4.7GB at the low end to as high as 17GB. The high capacities allow DVDs to contain so much more information, aside from the songs and movies, compared to CDs.
Before the advent of DVDs, the compact disc has totally dominated the media market. The CDs most prominent advantage over cassette and VHS tapes is the ability to jump to certain areas of the disc without needing to rewind or forward the medium. The digital format of storage also meant that there is no deterioration of data stored no matter how many times you play it back. CDs also became the preferred media for selling software and computer programs.
When the DVD format was introduced, it wasn’t intended to replace the CD in the audio market. The high capacity of the DVD did not provide enough of a reason to move from CDs to DVDs for audio. But Video and Software programs that were usually stored in two or more CDs can now be placed in a single DVD. DVDs even allowed movie makers to add bonus materials into DVD versions of theirs movies. Stuff like behind the scene videos and outtakes can be found in DVDs but not in CDs.
In terms of hardware, DVD players are backwards compatible and they can play all CDs. While, understandably, CD players cannot play DVDs. The backward compatibility of DVD players allowed most music albums to still be published in CDs instead of DVDs. The capacity of CDs is usually sufficient to hold an entire album and moving to DVDs would simply mean a higher cost with very little gain. Although there are already some music albums that are being sold in DVDs, they justify this by adding extra content like music videos aside from the audio only tracks.
Summary:
1.  DVDs have over 6 times more capacity than CDs at the minimum
2. Â DVDs are preferred for movies and Software
3. Â CDs are still the preferred in publishing music albums because of cost
4. DVD players can play both CDs and DVDs while CD players can only play CDs.