Disk Utility is Apple's go-to macOS app for finding and repairing common disk errors, but if it's your Mac's internal disk that's the problem, then your Mac might not even start up into macOS.

You are about to transfer some important files from an external drive to your Mac, and suddenly you get the message “Disk Not Ejected Properly” The transfer fails, and you have to start all over again ...

James Duff reports routinely inaccurate reporting of OS version numbers through Mac OS 9's Startup Disk control panel: "In a nutshell, my Startup Disk control panel reports the wrong system version in ...