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A bit rude, but he's right.

Also OS X server comes on different macs, like the XServe. It does exactly what you think it does.
 
OS X Server and OS X Client are based on the same kernel and can do exactly the same things.

OS X Server gives you certain additional things:

•GUI tools to easily modify Apache/File Sharing/Print Serving configurations
•Quicktime Streaming Server
•WebObjects

You can serve a website on OS X Client, but it will take lots of work in Terminal do make it as powerful as OS X Server.
 
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