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Virtualization is a technology that combines or divides computing resources to present one or many operating environments using methodologies like hardware and software partitioning or aggregation, partial or complete machine simulation, emulation, time-sharing, and others. Virtualization technologies find important applications over a wide range of areas such as server consolidation, secure computing platforms, supporting multiple operating systems, kernel debugging and development, system migration, etc, resulting in widespread usage. Most of them present similar operating environments to the end user; however, they tend to vary widely in their levels of abstraction they operate at and the underlying architecture.

This paper surveys a wide range of virtualization technologies, analyzes their architecture and implementation, and proposes a taxonomy to categorize them on the basis of their abstraction levels. The paper identifies the following abstraction levels: instruction set level, hardware abstraction layer (HAL) level, operating system level, library level and application level virtual machines. It studies examples from each of the categories and provides relative comparisons. It also gives a broader perpective of the virtualization technologies and gives an insight that can be extended to accommodate future virtualization technologies under this taxonomy. The paper proposes the concept of an extremely lightweight technology, which we call as Featherweight Virtual Machine (FVM), that can be used to ”try out” untrusted programs in a realistic environment without causing any permanent damage to the system. Finally, it demonstrates FVM’s effectiveness by applying it to two applications: secure mobile code execution and automatic clean uninstall of Windows programs.