It didn't take long for the masses of Mac fans to grow impatient with fiddling around with System Preferences and control panels just to go back and forth between 9 and X.
Here are three ways to reduce the number of steps.
If you have both Mac OS 9 and Mac OS X installed on the same hard drive or disk partition, use this sensational shortcut: Just hold down the letter X key while the Mac is starting up. (Hold it down until the Mac stops chiming.) You go straight to Mac OS X.
The only downside to the X key trick is that it's one-way. You can't, for example, hold down the 9 key to start up in Mac OS 9 again—at least not if 9 and X are on the same drive.
If you've installed 9 and X on two different drives or partitions, though, you can enjoy the D key trick. It works in either of these two situations:
You have two hard drives. You've installed Mac OS 9 on the internal hard drive, and Mac OS X on an external.
You have one hard drive, but you've partitioned it (divided it into two or more "virtual disks," each with its own icon). You'll find instructions for setting up multiple partitions—and installing different operating system versions on them—in Appendix A.
But here's the key point: You've installed Mac OS 9 on the first partition.
Once you've arranged things like this, leave your System Preferences set so that Mac OS X is the startup disk, as described earlier. But on those occasions when you want ...