Add an External Drive to Your MacBook
Most people who upgrade their MacBook's existing hard drive do so because they need extra space; however, you might also need to add a hard drive to your system that can go mobile whenever necessary. Unlike an internal drive — which resides hidden inside your MacBook’s case — an external drive is a lean, mean, self-contained traveling storage machine that’s perfect for road warriors, especially those using Lion’s Time Machine backup feature.
Although most external drives carry their own power supply, some models actually don’t need a separate power cord because they draw their power through your Mac’s Universal Serial Bus (USB), FireWire port, or Thunderbolt port. External drives also have a number of other advantages:
No installation hassle: You can easily install a Thunderbolt, USB or FireWire drive in seconds. Simply plug in the drive to the proper connector on your MacBook, connect the power supply (if necessary), and turn it on.
No extra space needed: Naturally, MacBooks simply don’t have the internal space for another drive. Therefore, if you want to keep your existing internal drive as-is while you’re adding more storage, an external drive is your only choice.
File sharing with ease: With an external drive, you can easily share your data between multiple Macs, even if they’re not connected over a network.
Safe from prying eyes: Unlike an internal drive, external drives can be secured in a different spot, away from your MacBook. Take your sensitive information home with you or lock it in a safe.
After you plug in an external drive, Mac OS X displays it just like any other hard drive volume. Note that the drive bears the FireWire symbol as an icon, marking it as an external drive.
Most modern Mac laptops (except for the MacBook Air) have a DVD-R drive, which makes it easy to send up to 8.5 GB of data through the mail on a single recordable disc. No one wants to box up an expensive external hard drive (or even a USB flash drive) to transport 4GB worth of photos to Aunt Martha!