index-sequential access method (IBM) (ISAM)

The Index Sequential Access Method (ISAM) is a relatively old file management system with a sequential access to databases.

In this index sequential database query, an index is created that searches each record sequentially, either in time order or randomly. Each index defines a different order. The database can be indexed by specific search terms, such as zip code, name, or city. The files are presorted after indexing and the smaller indexes are searched first.

Index Sequential Access Method was developed by IBM back in the 1960s, but it has some performance limitations, such as dynamic changes associated with frequent insertion and deletion of files.