The original storage engine in MySQL was the ISAM engine. It was the only storage engine available until MySQL 3.23, when the improved MyISAM engine was introduced as the default. ISAM is deprecated. As of MySQL 4.1, it is included in the source but not enabled in binary distributions. It is not available in MySQL 5.0. Embedded MySQL server versions do not support ISAM tables by default.

Due to the deprecated status of ISAM, and because MyISAM is an improvement over ISAM, you are advised to convert any remaining ISAM tables to MyISAM as soon as possible. To convert an ISAM table to a MyISAM table, use an ALTER TABLE statement:

mysql> ALTER TABLE tbl_name TYPE = MYISAM;

For more information about MyISAM, see Section 13.1, “The MyISAM Storage Engine”.

Each ISAM table is stored on disk in three files. The files have names that begin with the table name and have an extension to indicate the file type. An .frm file stores the table definition. The data file has an .ISD extension. The index file has an .ISM extension.

ISAM uses B-tree indexes.

You can check or repair ISAM tables with the isamchk utility. See Section 6.6.1, “Using myisamchk for Crash Recovery”.

ISAM has the following properties:

Many of the properties of MyISAM tables are also true for ISAM tables. However, there are also many differences. The following list describes some of the ways that ISAM is distinct from MyISAM: