Virtualization

hypervisor is layer that provides the vitualization capability to create vm and their communication with hardware.

Two types of hypervisors
 
Type 1 Hypervisor

hypervisor running on bare metal hardware
Part of kernel running on directly on kernel
VM ESX.
IBM Z/VM

Type 2 Hypervisor

Hypervisor Running on BaseOS OR HostOS
VMWare workstation and server , parallel Desktop MS Virtual Server.

Type 3: Hybird Hyper-visor

Xen is Hybird.

** Emulator
  it is software which emulates Piece of hardware for its VM.

**Domain:
 Any Virtual machine running on Hypervisor.

Domain-0 previlaged ( thick domain)
Domain-U Unprevilged (  Thin Domain)
 all virualization machines created by D-0

**Physical Address Extension: PAE

**Intel VT-x

Paravirtual Machine.there is no hardware emulation. vm created using xen para-virtualization.
xen hypervisor acts on behalf of pvm

* hardware virtual machine HVM
kernel virtual machine kvm





*******Why Not Vitualization******
Administration of VMs , sensitive, multiple traffic , multiple ips .
networking issues