Difference between "process virtual machine" with "system virtual machine"

Question

What's the difference between process virtual machine with system virtual machine?

My guess is that process VM is not providing a kind of an operating system for the whole application for that OS, rather providing an environment for some specific application. And system VM is providing an environment for an OS to be installed just like VirtualBox.
Am I getting it correct?

Another question is the difference between the two different implementation of system VM: hosted vs. stand-alone.

I'm a beginner studying OS, so easy and understandable answer would be greatly appreciated :)

Answer 1

The following is from http://airccse.org/journal/jcsit/5113ijcsit11.pdf : System Virtual Machines A System Virtual Machine gives a complete virtual hardware platform with support for execution of a complete operating system (OS). The advantage of using System VM are:

• Multiple Operating System environments can run in parallel on the same piece of hardware in strong isolation from each other.
• The VM can provide an instruction set architecture (ISA) that is slightly different from that of the real machine

The main draw backs are:

• Since the VM indirectly accesses the same hardware the efficiency is compromised.
• Multiply VMs running in parallel on the same physical machine may result in varied performance depending on the workload imposed on the system. Implementing proper isolation techniques may address this drawback.

Answer 2

A Process virtual machine, sometimes called an application virtual machine, runs as a normal application inside a host OS and supports a single process. It is created when that process is started and destroyed when it exits. Its purpose is to provide a platform-independent programming environment that abstracts away details of the underlying hardware or operating system, and allows a program to execute in the same way on any platform.

A System virtual machine provides a complete system platform which supports the execution of a complete operating system (OS),Just like you said VirtualBox is one example.

A Host virtual machine is the server component of a virtual machine , which provides computing resources in the underlying hardware to support guest virtual machine (guest VM).