As the title says, are there limits (if any) for session variables or they\'re considered as usual variables and can store equal amount of data?
I\'m lookin
It is completely specific to your web-server. For Apache, look here:
http://httpd.apache.org/docs/trunk/mod/mod_session.html
It even allows sessions to be stored in database by using mod_session_dbd. Therefore physical limits like 1 file per session can be overcome. Moreover, Apache can be configured to keep track of per user sessions stored on a particular server or group of servers for scalability.