What Am I Riddles

Question: I have all of your knowledge but could fit in your hands.

What am I?

Question: You are my brother, but I am not your brother. Who am I?

Question: No matter how much rain comes down on it it won't get any wetter.

What is it?

Question: I have Eighty-eight keys but cannot open a single door?

What am I?

Question: I fly, yet I have no wings. I cry, yet I have no eyes. Darkness follows me; lower light I never see.

What am I?