You need to have a DVD-ROM or a DVD burner in order to be able to play/read DVDs. However, most DVD players are DVD/CD combo units, so what you refer to as a CD tray may in fact have the capability of playing DVDs as well. If you know the make and model number of your computer that will tell us what features you have available to you. It's usually stated on the front of your computer tower.
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I don't know what technical info to provide, or where to get it, but if someone can help, I'll find it.