The Internal/External Drive Switcher is a two-piece adapter for the Apple IIc, providing an easy way to select which floppy drive will act as Drive 1. It’s a convenience option for the IIc, which normally can only boot from its internal 5.25 inch floppy drive. In the Drive Switcher’s “swapped” mode, an external Floppy Emu disk emulator will act as Drive 1, and the internal floppy drive will act as Drive 2. In normal mode, the internal floppy will act as Drive 1 and Floppy Emu as Drive 2.
The Drive Switcher isn’t required, but it makes everything more convenient for a Floppy Emu on the Apple IIc, when emulating a 5.25 inch floppy disk drive. Before now, the best alternative was to disconnect the internal floppy drive, and connect the Floppy Emu to Apple IIc the motherboard. While this worked fine for the Floppy Emu, it meant IIc owners forfeited their ability to use the internal drive. With the introduction of the Drive Switcher, IIc owners now have the best of both options.