PHP4 is packed with good features. One of the most popular is session variables. These are variables that persist throughout a session, as the user moves from page to page. Session variables are great holders of state information and other useful stuff. PHP4's session variables are stored in files by default. However for true scalability, it is better to store this data in a database using a database wrapper library like ADODB. ADODB supports Oracle, MySQL, PostgreSQL, Interbase, MSSQL, VFP, Access, ADO.