MySQL data structure

[Asaf Maruf Ali]

Hello.

I am interested to know the structure of MySQL. My ref book "MySQL and mSQL" by 
O'Reilly states that for a table named book under a database Test following is the 
structure:


book.ISM
book.ISD and
book. frm

On my system MySQL 3.23.27 beta the structure is different.

book.MYI
book.MYD
book.frm

Any suggestions would be welcome. 
Suggestions on backing up the MySQL db as well.

Anyone has experience of hosting MySQL/PHP ? Any recommended server/host/company?


Thanks in advance