There are two kinds of VMM(Virtual Machine Monitor) accord to their virtualization level, system VM and process VM.
I know that KVM is a "system VM", and what about QEMU?
Is it same as KVM?

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    QEMU (short for Quick Emulator) is a free and open-source hosted hypervisor that performs hardware virtualization (not to be confused with hardware-assisted virtualization). QEMU needs KVM’s performance boost. However, it is clear that KVM by itself cannot provide the complete virtualization – Nullpointer Dec 26 '15 at 14:22

QEMU can actually fonction in either mode, providing full system emulation (and running a complete operating system) or only CPU emulation for a single process.

QEMU can also function with or without KVM; if KVM is available, QEMU can use it as an accelerator.

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  • So it will play a role as process system VM when executing program by QEMU on the command line? Since it emulate only for a single process? – proX Dec 27 '15 at 9:27
  • No, it's either/or; if you start qemu-system-... then it's a full VM (or system VM), if you start qemu-... (e.g. qemu-i386) then it's a process VM. – Stephen Kitt Dec 28 '15 at 10:41
  • Thanks. Is there any difference between "qemu-system-i386" and "qemu-i386"? Since the former is so-called system VM and the latter is process VM just because of the key word "system"? – proX Dec 28 '15 at 14:33
  • qemu-system-i386 starts an i386-based system emulator (or VM), with all the usual peripherals; it expects to boot a full operating system. qemu-i386 runs the given binary by translating it, it only emulates an i386 CPU without any peripherals and expects to be able to run the given binary on the current operating system. – Stephen Kitt Dec 29 '15 at 19:28

KVM is built on to of QEMU and QEMU is a system VM as you are calling it.

I do not know your source of information, but from https://en.wikipedia.org/wiki/Virtual_machine

A system virtual machine provides a complete system platform which supports the execution of a complete operating system (OS).

and http://qemu.weilnetz.de/qemu-doc.html#intro_005ffeatures

Full system emulation. In this mode, QEMU emulates a full system (for example a PC), including one or several processors and various peripherals. It can be used to launch different Operating Systems without rebooting the PC or to debug system code.

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