By fall, Chrysler, Infiniti, and Mercedes-Benz cars will have them to use for navigation and for entertainment. Since early this year, Mercedes-Benz has been shipping the $85,000 S-Class with a 20GB hard drive for navigation. And Chrysler and Infiniti recently detailed plans to ship cars that will have hard drives for both navigation and music storage.

With Chrysler MyGiG , built into the Sebring, Dodge Nitro, and Jeep Wrangler, you can rip CDs to the hard disk or slip a USB key into a jack on the dash: The audio system offloads MP3 and WMA tunes to the hard disk. Infiniti, with its Bose-designed Studio on Wheels system, lets you rip CDs, and you can also load music from memory keys. Both have the Gracenote music identification system, which adds artist, track, and album information to the music files. MyGig also lets you upload photos for a slideshow and personal screensaver.

Hard drive technology should lower the cost of the car you want. If a car has a ruggedized hard drive (add $50 to $75), you'll no longer need a dedicated DVD reader for the navigation disc (subtract $25). The in-dash CD drive now has to be a DVD drive to read the nav disc (add $5), but when you've got storage for 150 CDs on the hard drive (assuming a 20GB drive with half the memory allocated for music), you no longer have much need for a six-disc CD changer (subtract $100).

The hard disk is just one part of a new-technology infotainment system; you also need a connection to outside data. In addition to an optical drive, every car needs to have a port for USB keys. The USB jack should also be able to connect with music players, including the iPod, and let you control your music via the radio. A key could also transfer your Outlook address book for use by the navigation system and hands-free phone.

With these new memory options integrated into your car, you may just decide to leave your laptop at home.