Here’s a little bit of knowledge that might come in handy in certain situations—for instance, if the drive on your main Mac has died, and you have a CD-based software program you absolutely must install now. You might think all is lost, but that’s not necessarily the case—as long as you have another Mac in the house.
One of the Mac’s more interesting features is something known as FireWire target disk mode. Boot one machine in target disk mode (hold T while booting), then connect it to another with a FireWire cable, and you’ve now got the world’s most expensive FireWire disk—the Mac booted in target disk mode will appear just like a FireWire hard drive to the other Mac.
Using target disk mode is a great way to transfer lots of data between two Macs, because FireWire connections are super fast. (Not all Macs can be put into target disk mode; the page linked above includes a list of applicable models.) But there’s an added bonus with most newer Macs: you’ll have access not only to the hard drive, but the CD/DVD drive as well. As proof, the image at left (click it for a larger version) shows Disk Utility running on my Mac Pro. Down near the bottom, note the two FireWire devices. The first is the hard drive in the MacBook Pro (split into two partitions for Windows and OS X). Below that, though, you’ll see the DVD-R drive, complete with Charlie and the Chocolate Factory loaded.
Now, you probably won’t be able to use this drive for burning—I wasn’t, at any rate. Nor was I able to use it to watch a DVD movie (in either DVD Player or VLC). But it is a usable CD/DVD drive, meaning you can install that urgently-needed software package, or grab some files off of a burned backup disc. You could also, in theory, run an installation disc off your virtual CD/DVD drive, though I haven’t tested such a thing myself. And since basically any Mac with a FireWire port and Mac OS 8.6 or newer on it can see target disk mode machines, you can use this trick to read a DVD disc in an older machine that might only have a CD unit.
When you’re done using the target disk mode machine, eject any mounted volumes on the host Mac, then you can power off the target machine and reboot into normal OS X mode by powering up again.