Now is the era of cloud computing where internet based data are handled from remote places. Data is being entered, stored, processed, deposited and backed up all at the central servers located in specific buildings. Data center is a place where all these servers are gathered in compliance with art of technology. We have some limitations regarding knowledge about the architectures of data center. This article reveals some ideas about data center architectures and its components. Specially, this paper gives emphasis on explaining data center tier levels and its applications.