The number tells robots and humans what type of vehicle it is, whether it has a multiple-CD changer and what color the seats will be.

FORBES: Overdrive

If leather seats come only with a package that includes a six-disc CD changer, the customer won't be able to unbundle the options and pick only what he wants.

FORBES: Just in Time Meets Just Right

One Saturday I sat alone on the floor in our tiny apartment, piecing a quilt, when the CD changer switched to a Mos Def album that Adam had been listening to a few days before.

NPR: Finding Hope in Hip-Hop

Think of it: you can toss that kludgey 20-disk CD-changer out of the car boot and still have every tune you own at your disposal when on the road.

CNN: All Music, All the Time