مقدمه انگلیسی :

In 2009 NIST3 defined Cloud Computing as “a model for enabling convenient, on-demand network access to a shared pool of configurable computing resources that can be rapidly provisioned and released with minimal management effort or service provider interaction. Pay per usage, Virtualization, on demand access, flexibility and reduced hardware and maintenance cost are some of the factors contributing to popularity of cloud computing1 2. Platform as a Service (PaaS), Infrastructure as a Service (IaaS), and Software as a Service (SaaS) are service models of cloud computing. SaaS provides ability to run and use the software/ application without the need to install it on your own machine. IaaS makes use of virtualization technology to provide Infrastructure by sharing the hardware with many customers or tenants 3. Virtualization plays a major part in cloud computing by making effective and systematic use of the available hardware. Recently Virtualization is used at various stages like networks, CPU, memory, storage etc. It increases the availability of system and also reduces cost and present a superior flexible system.