You could solder together a machine whose electronics obeyed Basic directly. Or you could build a mechanical system that did. Or you could compile Basic on a VAX, or PC,...; or you could interpret it. At one level, all have the same behaviour: they are virtual machines for Basic. Something is a virtual machine for X if it behaves like X, but that behaviour is actually implemented by software - by programming lower down - rather than by hardware. So Newell would have said in 1972 that the brain's neural hardware implemented a production-system virtual machine.
To reduce the amount of complexity they have to think about, engineers and programmers often implement complex systems in layers. E.g.
So we have a hierarchy of virtual machines or functional architectures. See Chapter X of Hofstadter's Gödel, Escher, Bach (Penguin 1981: PSY KH:H 67) for further discussion.
Can we analyse biological systems this way