Where are cookies actually stored on the hard disk?

This depends on the user's browser and OS.
In the case of Netscape with Windows OS,all the cookies are stored in a single file calledcookies.txt c:\Program Files\Netscape\Users\username\cookies.txt
In the case of IE,each cookie is stored in a separate file namely username@website.txt. c:\Windows\Cookies\username@Website.txt