Just google some images mate, you'll see the uppermost part of the bore is not connected to the outer wall of the block.... thats open.
Partial open normaly has a connection to the block inbetween each cylinder.
Closed(like a yb) has a connection....all the way round sortov. It has the waterjacket holes perferating the deck.
Bad explanation but you'll suss it from the pic straight away.