Blinking folder icon

The blinking folder icon (formerly a blinking floppy icon) appears on Macintosh computers when no startup disk can be found during the process of booting. This icon is stored on the Macintosh Toolbox ROM chip on Old World ROM Macs. In New World ROM Macs, it is stored with Open Firmware on the logic board. On Intel-based Macs, it is stored as part of EFI firmware.

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.