Even though sorting and indexing are not numerical algorithms by nature, they are essential for manipulating large amounts of data, stored either in the main computer memory or as magnetic files. The data structures are generally organized as collections of records or tuples, each composed of several fields of various types. Perhaps, the most common example of a data structure is one composed of records of personal data, with the fields holding separate details such as given name, family name, age, E-mail address, and so on. The information from each record that is used for classifying the records is called key and it is typically identified with one of the fields, which can be numeric or nonnumeric. The order of the records in the collection is indicated by an index.