To know for sure what kind of radio was originally in *your* 1999 Chevy Malibu, you'd need to:
* Check the radio itself: Look at the faceplate for the model number. This number will help you identify the exact radio.
* Look at the owner's manual (if you have it): The manual should specify the radio model installed.
* Check the vehicle's build sheet (if you can find it): This detailed document lists all the options installed at the factory.
Without more information about your specific Malibu, it's impossible to say precisely which radio it originally had.