Know on which platform a server Is running i.e. linux/Windows/Mac ?

To know whether a server is running on Linux/Windows/Mac platform, we have to just ping the website. If,
TTL<64--> Server Running on Linux Platform.
128>TTL>64--> Server Running on Windows Platform.
TTL>128--> Server Running on Mac Platform.

TTL(Time To Live): It is the expiration value of DNS data. It is specified in seconds.

e.g. If we want to know on which platform the GOOGLE web server is Running, we just have to:

Go to START-->RUN-->CMD-->Type ping www.google.com

As the TTL<64, the GOOGLE web server is running on Linux Platform.

In this way we can check every website and know on which Platform these web servers are Running.