Abstract: With the initiation of internet in the 1990s to the present day facilities of universal computing, the internet has reformed the computing world in a drastic way. It has travelled from the concept of parallel computing to distributed computing to cluster computing to grid computing to utility computing to virtualization and recently to cloud computing, in future Internet of Things. Virtualization and utility computing can be stated as key concept of cloud. As cloud computing can be specified as a realization of utility computing. Although the idea of cloud computing has been around for quite some time, it is an evolving field of computer science. Since the evolution of cloud computing: Load balancing, energy management, VM migration, server consolidation, cost modelling and security issues are the popular research topic in this field. Deploying real cloud for testing or for commercial use is very costly. Cloud computing model have complex provisioning, composition, configuration, and deployment requirements. Evaluating the performance of Cloud provisioning policies, application workload models, and resources performance models in a repeatable and controllable manner under varying system and user configurations and requirements is difficult to accomplish. To overcome this challenge, cloud simulator is needed.In this paper basic of cloud simulator is discussed, and major focus is on cloudsim- a simulator for management of vm.The CloudSim toolkit supports both system and behaviour modeling of Cloud system components such as data centers, virtual machines (VMs) and resource provisioning policies. It implements generic application provisioning techniques that can be extended with ease and limited effort. Currently, it supports modeling and simulation of Cloud computing environments consisting of both single and inter-networked clouds (federation of clouds). In this paper how cloudsim work, its architectural design, highlighting important features and give brief overview of its functionalities is presented.

Keywords: Cloud computing; modelling and simulation; Virtual machines; VM management, millions of instruction per second (mips)