ISAM (Indexed Sequential Access Method)

What is ISAM (Indexed Sequential Access Method)?

ISAM (Indexed Sequential Access Method) is a file management system developed at IBM in the 1960s to access records either sequentially, in the order they were entered or randomly with an index.

Each index defines a different ordering of the records. An employee database may have several indexes, based on the information being sought. For example, a name index may order employees alphabetically by last name, while a department index may order employees by their department. A key is specified in each index. For an alphabetical index of employee names, the last name field is the key.

ISAM was developed prior to Virtual Storage Access Method (VSAM) and relational databases. ISAM has been phased out with VSAM, but it still might be in use with older systems that do not require large and complex workloads.