There is a flag in the MyISAM file that indicates whether or not the table was closed correctly. This will soon be used for automatic repair in the MySQL server. Dynamic size rows will now be much less fragmented when mixing deletes with updates and inserts. This is done by automatically combining adjacent deleted blocks and by extending blocks if the next block is deleted. MyISAM also supports the following things, which MySQL will be able to use in the near future.
All key segments have their own language definition.
This will enable MySQL to have different language definitions per column. You can also use the deprecated ISAM table type. This will disappear in rather soon since 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 file with the .ISD extension.