Shut Down Warning is an option which could be enabled through the General Controls control panel under all versions of the Classic Mac OS. If the Shut Down Warning option was active, a warning would appear when the Macintosh was restarted using the following methods: Beginning with Mac OS 8.5, the hard drive would additionally be checked for any defects. The phrase Shut Down Warning was altered to read Check Disk in the General Controls control panel beginning with Mac OS 9.1.