Tells the computer what hard drive to look for when it boots. Unless you have more than one hard drive, deselect your hard drive by clicking in the area surrounding it. You Mac will still boot, but this will make it easier if you ever have to work from an external drive. If you have a third-party drive that has been partitioned with APS PowerTools, you will need to use the APS Mounter control panel to change your startup partition. Works on all Mac OS-based computers that use System 7.5.
