  An emerging internet based super computing model is represented by cloud
computing. Cloud computing is the convergence and evolution of several concepts
from virtualization, distributed storage, grid, and automation management to
enable a more flexible approach for deploying and scaling applications.
However, cloud computing moves the application software and databases to the
large data centers, where the management of the data and services may not be
fully trustworthy. The concept of cloud computing on the basis of the various
definitions available in the industry and the characteristics of cloud
computing are being analyzed in this paper. The paper also describes the main
cloud service providers and their products followed by primary cloud computing
operating systems.
