Canon EOS-1D X Mark II DSLR Camera (Body Only) - Manual (Page 5)

5
The following cards can be used with the camera regardless of
capacity:
If the card is new or was previously formatted (initialized)
by another camera or computer, format the card with this camera
(p.74).
CF (CompactFlash) cards
* Type I, UDMA Mode 7 supported.
CFast card
* CFast 2.0 supported.
When shooting movies, use a large-capacity card with good enough
performances (fast enough reading and writing speeds) to handle the
movie recording quality. For details, see page 316.
Compatible Cards
Cards that Can Record Movies
In this manual, “CF card” refers to CompactFlash cards and “CFast card”
refers to CFast memory cards. “Card” refers to all memory cards.
*
The camera does not come with a card for recording images/movies.
Please purchase it separately.