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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.

Question: How do they work
Self-contained rewrite: How do virtual machines work?