Can anyone suugest why linux is prefered as servers in most of the companies than windows or other OS
Is there any reason behind it other than this reason(opensource).
It's the choice of many for a good few reasons.
Firstly, it's open source.
It's free (cost wise).
It's more secure. When security issues are found, they are generally corrected quickly. More quickly than the leading alternative OS.
It works nicely with other popular open source web technologies, such as Apache, MySQL, PHP, etc.
It's more stable. You can have longer uptime more stability.
There's a lot of support with an ever increasing userbase. Mailing lists, forums, irc channels... If you ever have a problem, you can generally get it fixed with help from your peers.
It has true multi-user capabilities.
It's not vulnerable to virus attacks.
It uses less memory and CPU resources than the other alternatives (or windows at least). Imagine, you have a server with a desktop constantly running. Video graphics, icons, full blown GUI (and explorer.exe doesn't have the smallest of footprints). Why? In linux, you don't need to have a desktop environment running, or even installed. Your users (the webmasters) won't be using it!
Better remote admin capabilities. You don't want to fuss around with VNC. Just SSH in and do all the real work through a shell. Less bandwidth, less messing and all the power comes in the shell anyway.
There's a few, I'm sure other people could add a lot more.