Canon EOS M EF-M 22mm STM Kit Instruction Manual page 43

Execute [Format card] in the following cases:
The card is new.
The card was formatted by a different camera or a computer.
The card is full with images or data.
A card error is displayed (9?).
What is low-level formatting?
Perform low-level formatting if the card's recording or reading speed seems slow
or if you want to totally erase all data in the card.
Since low-level formatting will format all recordable sectors in the card, the
formatting will take slightly longer than normal formatting.
You can stop the low-level formatting by selecting [Cancel]. Even in this case,
normal formatting will be completed and you can use the card as usual.
When the card is formatted or data is erased, only the file management
information is changed. The actual data is not completely erased. Be aware of
this when selling or discarding the card. When discarding the card, execute
low-level formatting or destroy the card physically to prevent the personal
data from being leaked.
Before using a new Eye-Fi card, the software in the card must be
installed in your computer. Then format the card with the camera.
The card capacity displayed on the card format screen may be smaller than
the capacity indicated on the card.
This device incorporates exFAT technology licensed from Microsoft.
3 Formatting the Card
43