**TO ALL LEXUS OWNERS**why are there two disc slots behind the navigation...

[arizona_iced_te4]

...on the lexus es330? to any owners of the lexus es330 or i'm guessing any lexus that has navigation, why are there two slots to put in discs? i mean the 6 cd changer is in the arm rest and behind the screen is for the navigation disc but then there is one more slot to put another disc...........is it a DVD player??? i dont wanna mess with it until i get a good answer lol (the owners manual is useless)