Guest vs Host:

• Host – usually runs on physical hardware, lower level.
• Guest – runs on the virtual/virtualized environment, upper level.

Virtualization types:

• Full virtualization –  virtualize all the devices!
  • Can run almost all the operating systems without any modifications.
  • Emulate all the devicesn.
  • Slower than Paravirtualization and Operating-system-level virtualization.
  • Software Emulation (Without Hardware-Assisted-Virtualization)
    • Very Slow.
    • Need to do some jobs like binary translation or software instruction decode, will have a heavy overhead, is very inefficiet.
  • Paravirtualization on HVM
    • Full virtualization with paravirtualization drivers.
• Paravirtualization(PV) – use modified kernel to interact with the special interface
  • Guest knows it’s a guest on the host, the guest will communicate with hypervisor.
  • Use hypercall (call to hypervisor) as its system call.
  • Hard(almost impossible) to modify the kernel of closed-source operating systems like Windows to use this method.
  • Faster than full virtualization but slower than operating-system-level virtualization.
• Hardware-Assisted-Virtualization (HVM, HAV)
  • Using help from hardware capabilities.
  • Faster than Software Emulation.
  • Technic examples
    • AMD-V (Pacifica)
    • Intel VT-x (Vanderpool)
• Operating-system-level virtualization – don’t really virtualize the devices
  • Fastest – SUPER FAST!!!
  • Isolate different user space instances.
  • Don’t need hardware support.
  • Must run on the same kernel
    • Means bad compatibility.
  • Examples:
    • LXC
    • Docker
    • OpenVZ
    • FreeBSD Jail
    • Linux VServer
• Partial virtualization – need be confirmed, not a usual type
  • The section of partial virtualization on wikipedia said that “This section does not cite any references or sources”.

Type-1 vs type-2 hypervisor:

• Type-1
  • Native/Bare-matel
  • Runs directly on the real hareware, directly control the hardware resources.
  • Examples:
    • XenServer
    • Microsoft Hyper-V
    • VMware ESX/ESXi
• Type-2
  • Runs on an existing operating system.
  • Examples:
    • Oracle VirtualBox
    • vmware player

Wikipedia also use Application/Environment and OS level to distinguish different types of virtualization:

• Application-level
  • Sandbox
• Environment-level
  • Containers
• OS-level
  • Hypervisors

Common integrated virtualization solutions:

• XenServer
• OpenNode
• Proxmox VE
• Microsoft Hyper-V
• VMware ESX/ESXi
• Red Hat Enterprise Virtualization

Resources and references:

• Understanding full virtualization paravirtualization and hardware assist – vmware white paper
  • http://www.vmware.com/files/pdf/VMware_paravirtualization.pdf
• Virtualization on Wikipedia
  • https://en.wikipedia.org/wiki/Virtualization
• The Paravirtualization Spectrum
  • Explanations of Full virtualization, PV, HVM, PVH and PVHVM (so many terms here … a little bit too complex, ha)
  • Part 1: The Ends of the Spectrum
    • https://blog.xenproject.org/2012/10/23/the-paravirtualization-spectrum-part-1-the-ends-of-the-spectrum/
  • Part 2: From poles to a spectrum
    • https://blog.xenproject.org/2012/10/31/the-paravirtualization-spectrum-part-2-from-poles-to-a-spectrum/

source : https://blog.xenproject.org/2012/10/31/the-paravirtualization-spectrum-part-2-from-poles-to-a-spectrum/

Still learning, hope that there are not too many wrong things here … comments to point out mistakes/weak points are welcome!