webserver and application server
http://www.diffen.com/difference/Application_Server_vs_Web_Server
http://www.differencebetween.com/difference-between-web-server-and-vs-database-server/
http://www.acunetix.com/websitesecurity/webserver-security/
http://blog.csdn.net/keyeagle/article/details/6723408
出处:http://cnblogs.com/daishuguang