Introduction to Virtual Machines

Virtualization provides a way of relaxing the foregoing constraints and increasing flexibility. When a system, for example, a processor, memory, or input/output (I/O) device, is virtualized, its interface and all resources visible through the interface are mapped onto the interface and resources of a real system actually implementing it. Consequently, the real system is transformed so that it appears to be a different virtual system or even a set of multiple virtual systems. The concept of virtualization can be applied not only to subsystems such as disks, but to an entire machine. A virtual machine (VM) is implemented by adding a layer of software to a real machine to support the desired virtual machine's architecture. A wide variety of virtual machines exists to provide an equally wide variety of benefits. Multiple, replicated virtual machines can be implemented on a single hardware platform to provide individuals or user groups with their own operating system environments. The different system environments also provide isolation and enhanced security. A large multiprocessor server can be divided into smaller virtual servers, while retaining the ability to balance the use of hardware resources across the system.