A binary search is effective only when the list searched is ordered. It is efficient only when the list is dense—i.e. when records are in contiguous locations. It is easy to show that the maximum number of looks for a search <italic>L</italic> is given by [1]. <italic>L</italic> = [log<subscrpt>2</subscrpt><italic>N</italic>+1], (1) where <italic>N</italic> is the number of records in the list and the square bracket means “integral part of.”