Symbolic role-call vote????

I don't know much about how the convention voting works, past or up-coming. How do they announce in advance that they will nominate Sen. Obama, but still have a symbolic role-call vote on the floor? They say he "won" by something like 365 votes, I think. Will they order the delegates to vote a particular way during the roll-call, so that the vote totals show him 365 votes ahead of Clinton when it is over? What do they mean "symbolic"? Is the role-call a real vote or faked for this symbolism? That's more than one question, but about the same subject.