107. How to know the OS of web server

1)Goto the link below and find the IP Address of the website you want to gather information about. You may do this by writing its name in the Get IP box

http://www.selfseo.com/find_ip_address_of_a_website.php
(This step was optional just to tell you that it can be done this way also):-P
2)Goto run->type CMD

IN CMD type
ping Target _Website_Name . For Eg- ping google.com

or
ping target_website/computer_ip_address . For Eg:- 59.172.45.1


Now you will see several ping requests coming

Ping Google Server

We Are interested in seeing the TTL time which you can see at the end of each request in ping.
NOTE:- 
1) If TTL <64 then the server is Linux based
2) If TTL>64 but <128 then the server is Windows bsaed
3) TTL>128 Mac and others.From the above screenshot, it is clear that the servers of google are linux based.