Default Missing internal memory.

Hi guys,

Something strange happening (I guess)
On my 16 gb note 10.1 (n8010) I've got 11.66 gb of internal memory.
But only 7.26 is free.

What happens with the rest?
Or is this normal to have 4.4 gb internal storage used?
I've formatted my internal memory but nothing changed.

I understand that I am missing the 16 gb to 11.66 gb part. But why am I missing the rest?
So from 16 gb only 7.26 can be used used for storage.

I installed omega latest Jellybean ROM.