What is the difference between a server based operating system like OS X and Windows?

How is OS X a server based operating system and Widows is not?

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What is the difference between a server based operating system like OS X and Windows?
Windows has server titles, imaginatively called "Windows Server 2000, 2003, 2008" with different versions. The primary differences are in the capability of those server versions to perform a few very important tasks. For example, a Windows XP machine cannot act as a DNS, DHCP or Active Directory server, but Windows Server can perform all of those functions. I would imagine that OS X is server based in that it provides some of these functions that you normally would not find on a client version operating system.



That is just a small example, as there are vast differences in the capabilities of the server operating systems versus the client version operating systems (XP, Vista, etc.).