ISAM is a keyed storage structure in which data is sorted by the value in the key column, and the index is static.

ISAM is a more versatile storage structure than hash. It supports pattern matching, range scans, and partial key specification, as well as exact match retrievals.

ISAM tables use a static index that points to a static number of main pages. The index contains key ranges and pointers either to other index pages or to the data page where rows with that key range are found.

Using the Modify Table Structure dialog or the MODIFY statement, you can change any table to the ISAM storage structure. When you modify a table to ISAM, you must specify a key; otherwise, the first column is used as a key.