If a book is of the first printing would the ISBN end in 0 or 1?

If a book is of the first printing would the ISBN end in 0 or 1? and what does it mean if the ISBN end in 0?|||...I thought that ISBNs ended in whatever number they ended in, and that each one was unique to the book it was on... (For example, all the 'Silver Chair' books have the ISBN 0-590-25480-4.)