Here all have thier own importance-
Production Web Servers
This is the type of web server that most web designers are familiar with. A production server is a web server that hosts web pages and content that is ready for production. In other words, the content on a production web server is live to the internet or is ready to be delivered to the internet.
In a small company, the production server is where all the web pages live. Designers and developers test the pages either on their local machines or in hidden or password protected areas on the live server. When a page is ready to go live it is simply moved into place on the production server, either by FTP from the local hard drive or by moving the files from the hidden directory to the live directory.
Testing Server or QA Server
Testing servers are a useful addition to a website workflow because they provide you with a way to test new pages and designs on a web server that is not visible to customers (and competitors). Testing servers are set up to be identical to the live site and usually have some sort of version control set up on them to make sure that any changes are recorded. Most testing servers are set up behind a corporate firewall so that only employees can see them. But they can also be set up with password protection outside a firewall.
Development servers are very useful for sites that have a large development component, such as complex ecommerce sites and http://webdesign.about.com/web20/g/web-application-definition.htm. Development servers are used by the web development team to work on programming the back end of the website. They almost always have version or source code control systems for multiple team members to use and they provide a server environment for testing new scripts and programs.
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