Car CD players haven't quite gone extinct just yet, but they're slowly moving the way of the cassette as MP3 players and smart phones become our preferred way to play music. It's a natural evolution: These new storage mediums can hold far more music than audio CDs, and 3G and 4G data plans allow us to wirelessly stream music from services like Pandora. But MP3 players and smart phones have been designed with headphones in mind, which means car audio systems need a way to interface with these digital devices.
Luckily, many modern cars now include built-in connectors for these modern devices. We already covered Bluetooth, which can wirelessly link with some devices to play music or handle phone calls. Car manufacturers like Toyota offer optional auxiliary audio ports in their car stereos in the form of a 3.5mm (1/8-inch) mini stereo jack that can plug into anything with a headphone port [source: Toyota]. Others include USB ports that can also facilitate music playback from an iPod or similar device.
Don't have a brand new car with an auxiliary jack or USB port built in? Don't sweat it -- that's where our next car audio component, the head unit, comes in. With this one piece of equipment, you can dramatically improve the functionality of your car audio system.