The key information table contains 3 word entries that describe each key in the file and the first tables to be used in accessing the file with that key.

The first word of each key information table entry describes the key. It contains the same information in the same format as used for the ISAMKEYS file attribute discussed under “Indexed (KEYEDIO) File Attributes.”

The second word of each entry contains the relative segment address of the root table of the index tables for this key. If all the entries for this key will fit into a single table, the root table will be a fine table. Otherwise it will be a coarse table. The root table is the highest block in the hierarchical structure of index tables; it is the first table to be searched when accessing a file randomly.

The third word of each key information table entry contains the relative segment address of the first fine table for this key. It is used to find the first record when accessing the file sequentially.