In an IBM mainframe operating system , a data set is a named collection of data that contains individual data units organized (formatted) in a specific, IBM-prescribed way and accessed by a specific access method that is based on the data set organization. Types of data set organization include sequential, relative sequential, indexed sequential, and partitioned. Access methods include the Virtual Sequential Access Method ( VSAM ) and the Indexed Sequential Access Method ( ISAM ).
A data set corresponds to the concept of a file in other operating systems such as Linux and Windows 2000. Data set organization and file format are terms that have a close correspondence. A data set generally contains a collection of business data (names, salaries, sale figures, and so forth) whereas a file can contain many types of data (graphic images, audio data, video data, and so forth). For business data, the database is a newer alternative to the data set and the file.