In the last few years there has been a rapid exponential increase in computer processing power, communication and data storage. But still many complex and computation intensive problems, which cannot be solved by supercomputers. In the field of computing, a lot of changes have been observed due to the increased use and popularity of the Internet and the availability of high-speed networks. Resource sharing in a pure plug and play model that dramatically simplifies infrastructure planning is the promise of “Cloud computing‟. Cloud computing (1) is the development of parallel computing, distributed computing, grid computing and virtualization technologies which define the shape of a new era. Cloud computing is an emerging model of business computing. The paper aims to provide a means of understanding the model and exploring options available for complementing your technology and infrastructure needs. Also explore some of the basics of cloud computing with the aim of introducing aspects such as: Realities and risks of the model Components in the model and Characteristics and Usage of the model. This work aims to provide the ways to reduce security risk & also promotes the performance of cloud computing.