Blinking folder icon

The blinking folder icon appears on Macintosh computers when no startup disk can be found during the process of booting.

History
A variant of this icon existed since the original Macintosh 128K, which had no internal hard drive. It could only boot from a 400KB floppy drive, so this icon was originally a floppy disk with a blinking question mark.

Even after Macs had built-in hard drives, the floppy disk icon remained until the introduction of Macs with New World ROMs, when it was changed to a folder icon with a question mark repeatedly changing to a System Folder icon and back.

Intel-based Macs use a blinking folder with a question mark. The entire icon blinks.