Adafruit Feather M4 Express User Manual

The LED will flash. Then, the FEATHERBOOT drive will
disappear and a new disk drive called CIRCUITPY will
appear.
That's it, you're done! :)
Further Information
For more detailed info on installing CircuitPython, check out Installing CircuitPython (https://adafru.it/Amd).
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Adafruit Feather M4 Express Specifications

General

Brand	Adafruit
Model	Feather M4 Express
Category	Microcontrollers
Language	English