Blinking folder icon

The blinking folder icon is an icon that appears on Macintosh computers when no boot device can be found.

History
This icon existed since the original Macintosh, which had no internal hard drive, and could only boot from a 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 New World Macs, when it was changed to a folder with a question mark changing to the Finder icon.

Intel-based Macs feature a blinking folder with a question mark.