You can also use the deprecated ISAM table type. This will disappear
rather soon (probably in MySQL 4.1) because MyISAM is a better
implementation of the same thing. ISAM uses a B-tree index. The
index is stored in a file with the .ISM extension, and the data
is stored in a file with the .ISD extension. You can
check/repair ISAM tables with the isamchk utility. See Section 4.4.6.7.
ISAM has the following features/properties:
Compressed and fixed-length keys.
Fixed and dynamic record length.
16 keys with 16 key parts/key.
Max key length 256 (default).
Data is stored in machine format; this is fast, but is machine/OS-dependent.
Most of the things true for MyISAM tables are also true for ISAM tables. See Section 7.1. The major differences compared to MyISAM tables are:
ISAM tables are not binary-portable across OS/platforms.
Can’t handle tables > 4G.
Only support prefix compression on strings.
Smaller key limits.
Dynamic tables get more fragmented.
Tables are compressed with pack_isam rather than with myisampack.
If you want to convert an ISAM table to a MyISAM table so that you can use utilities such as mysqlcheck, use an ALTER TABLE statement:
mysql> ALTER TABLE tbl_name TYPE = MYISAM;
The embedded MySQL versions doesn’t support ISAM tables.
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