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What is the main function of a virtual machine?
The virtual machine function is a function for the realization of virtual machine environment. This function enables you to create multiple independent virtual machines on one physical machine by virtualizing resources such as the CPU, memory, network and disk that are installed on a physical machine.
What are a virtual machine's advantages?
The main advantages of virtual machines:Multiple OS environments can exist simultaneously on the same machine, isolated from each other;Virtual machine can offer an instruction set architecture that differs from real computer's;Easy maintenance, application provisioning, availability and convenient recovery.
Describe some of a virtual machine's disadvantages.
Disadvantages: Virtual machines are less efficient than real machines because they access the hardware indirectly. Running software on top of the host operating system means that it will have to request access to the hardware from the host.
How do virtual machines work?
A virtual machine app creates a virtualized environment—called, simply enough, a virtual machine—that behaves like a separate computer system, complete with virtual hardware devices. The VM runs as a process in a window on your current operating system.
What are the main types of Virtual Machines?
Examples of virtualization platforms adapted to such hardware include KVM, VMware Workstation, VMware Fusion, Hyper-V, Windows Virtual PC, Xen, Parallels Desktop for Mac, Oracle VM Server for SPARC, VirtualBox and Parallels Workstation.

Question: What is their role in cloud computing
Self-contained rewrite: What is the role of virtual machines in cloud computing?