A virtual machine is a piece of software that acts like a piece of hardware. This means that you could run a virtual machine in a Windows environment that emulates an Intel CPU, and then you could use that virtual machine to run a Linux operating system and all its applications. In effect you are running a Linux application in a Linux operating system as a Windows application in a Windows operating system. In this type of configuration, Windows is the host operating system, and Linux is the guest operating system. Virtual machines are available for almost all operating systems, Virtual machines are sophisticated pieces of software to completely emulate a piece of hardware. There is an unstated assumption when writing a piece of software to emulate a piece of hardware. What is that assumption?