Question

What is the difference between a hypervisor and a virtual machine?

Answer 1

and an emulator?

Answer 2

My guess is that the difference lies in the role that each are written for? The hypervisor can manage multiple virtual machines. Virtual machines run in isolation from the native OS of a system to simulate a software environment. Emulators do the same thing as VMs, though they can often be used to replicate not only the software environment but the hardware as well.

Answer 3

A hypervisor is also called a virtual machine manager. It takes care of presenting hardware to the virtualized OS and managing access to it.
The major difference between a VM and an emulator is that the emulator will provide a software version of a piece of hardware - it's a piece of software that acts to an OS or another software program as if a specific piece of hardware was available. A VM on the other hand, simply pipes access to the hardware the VM is running on. So, you could run a PowerPC application on an X86 processor using an emulator that acts like there's a PPC processor there, but not using a VM - because the VMM will simply provide access to the underlying x86 CPU.