What are the specific differences between an "emulator" and a "virtual machine"?
I see that they are different things but I really can't tell why. Some people say: "emulators are for games; virtual machines are for operating systems" I don't agree with this answers because there are emulators for platforms other than videogame consoles (AMIGA (?) )
Can you help me please?
Answer
Virtual machines make use of CPU self-virtualization, to whatever extent it exists, to provide a virtualized interface to the real hardware. Emulators emulate hardware without relying on the CPU being able to run code directly and redirect some operations to a hypervisor controlling the virtual container.
A specific x86 example might help: Bochs is an emulator, emulating an entire processor in software even when it's running on a compatible physical processor; qemu is also an emulator, although with the use of a kernel-side kqemu package it gained some limited virtualization capability when the emulated machine matched the physical hardware — but it could not really take advantage of full x86 self-virtualization, so it was a limited hypervisor; kvm is a virtual machine hypervisor.
A hypervisor could be said to "emulate" protected access; it doesn't emulate the processor, though, and it would be more correct to say that it mediates protected access.
Protected access means things like setting up page tables or reading/writing I/O ports. For the former, a hypervisor validates (and usually modifies, to match the hypervisor's own memory) the page table operation and performs the protected instruction itself; I/O operations are mapped to emulated device hardware instead of emulated CPU.
And just to complicate things, Wine is also more a hypervisor/virtual machine (albeit at a higher ABI level) than an emulator (hence "Wine Is Not an Emulator").