Canon EOS 6D Basic Instruction Manual page 50

Before You Start
Execute [Format card] in the following cases:
The card is new.
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The card was formatted by a different camera or a computer.
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The card is full with images or data.
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A card-related error is displayed.
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About Low-level Formatting
Perform low-level formatting if the card's recording or reading speed seems
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slow or if you want to totally erase data in the card.
Since low-level formatting will format all recordable sectors in the card, the
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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
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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
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than the capacity indicated on the card.
This device incorporates exFAT technology licensed from Microsoft.
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