Virtual machines can have resources allocated to them from the host without requiring that the virtual machine be powered down. This depends on the virtualization platform and guest OS specifically but in general you can "hot add" memory and CPU resources to virtual machines.
In computing, a virtual machine (VM) is an emulation of a computer system. Virtual machines are based on computer architectures and provide functionality of a physical computer. Their implementations may involve specialized hardware, software, or a combination.
There are different kinds of virtual machines, each with different functions:
System virtual machines (also termed full virtualization VMs) provide a substitute for a real machine. They provide functionality needed to execute entire operating systems. A hypervisor uses native …