I am not sure of why you are looking for this, and which version of MySQL you are using.
myisamchk to get the table information.
refer
http://dev.mysql.com/doc/refman/5.1/en/table-info.html for more information.
Datafile pointers The size of the data file pointer, in bytes. It is usually 2, 3, 4, or 5 bytes. Most tables manage with 2 bytes, but this cannot be controlled from MySQL yet. For fixed tables, this is a row address. For dynamic tables, this is a byte address.
A P Varma