Vol. 1, Issue 8, Part E (2015)

Abstract
Nowadays cloud computing is acquiring great deal of attention in users, markets, education and publications. Cloud is a group of servers that provide highly scalable services like SaaS, PaaS, IaaS to transform computing in business. Information stored in clouds is accessible from anywhere at any time. Cloud providers have storage, software and infrastructure facilities to run businesses effectively. Cloud computing is a dominant technology that facilitates businesses to become more connective, scalable, collaborative, real-time and productive. Cloud computing is based on the concept of virtualization and hence eliminates the need of a powerful configuration deployment by providing services at a reasonable price and hence this technology is very helpful for small organizations that cannot afford the cost of infrastructure and storage space. This robust technology has shifted the cost of managing hardware, software and computational infrastructure to third parties such as Google, Microsoft, Amazon. By shifting the costs of managing computational infrastructure to third parties, cloud computing has made it possible for individuals and small organizations to deploy world-wide services; all they need to pay is the marginal cost of actual resource usage. As all the data is being stored in clouds, security issues should be addressed properly. All the organizations have concerns about security, privacy, residency, unauthorized access, interception, interruption, modification, fabrication and non-repudiation. Security system of clouds should not be vulnerable to unauthorized data manipulation. By effectively implementing the pillars of cloud computing security of data over clouds could be ensured. This paper describes pillars, service models, deployment models and challenges of cloud computing to provide a better and common understanding of the subject.