A hard error is typically an error (such as the opening of a disk-drive door while a diskette is being read, or any similar kind of device error) that cannot be resolved by software. When a hard error occurs, the system default action is to prompt for user input by displaying a message in a pop-up window.

DosError disables the default action, foregoing the displayed message and causing an appropriate return value to be returned to whichever control-program function was running when the hard error occurred. The application must determine the appropriate response by referring to the return value.

DosError also enables the application to disable end-user notification if either a program exception or an untrapped numeric-processor exception occurs. However, if one of these exceptions occurs while user notification is disabled, the application will still be ended.

As with hard errors, the system default is that user notification for these exceptions is enabled.