Virtualization: Reference Models, Types, VM Lifecycle, and Technology Examples

This document covers Unit 2 of a Cloud Computing course, dedicated entirely to virtualization — one of the core enabling technologies of cloud computing. It opens with an introduction to virtualization, the virtualization reference model, and the key characteristics of a virtualized environment. The notes then differentiate between various types of virtualization, including storage virtualization, network virtualization, desktop virtualization, and application server virtualization, explaining how each type abstracts physical resources into flexible, software-defined equivalents. Real-world technology examples are covered in detail, including VMware's full virtualization reference model and Xen's architecture along with its guest operating system management approach, giving students practical insight into how virtualization is implemented in industry. A significant portion of the unit focuses on the Virtual Machine (VM) lifecycle, covering its definition and stages, VM migration concepts and techniques, VM consolidation strategies, and VM management practices — all critical for understanding how cloud providers efficiently allocate and move computing resources. The unit concludes with a balanced discussion of the advantages and disadvantages of virtualization, covering benefits like resource optimization and isolation, alongside challenges such as performance overhead and complexity. This unit is essential for understanding how physical hardware is abstracted to support scalable, multi-tenant cloud infrastructure. The notes are organized in a structured format, making them suitable as exam-prep or semester-end revision material. These notes were prepared by Diya during the 5th semester as part of the Computer Engineering curriculum, based on lectures and prescribed textbooks on cloud computing.