1. KVM (Kernel Virtual Machine): kernel module for user space programs to utilize the HW virtualization features of CPUs
   • exposes /dev/kvm (CPU, memory, I/O, network, maps video display back to host…)
2. QEMU: generic open source machine emulator and virtualizer
   • virtualizer: executes the guest code directly on the host CPU
   • userspace host using KVM (can also use Xen)
   • falls back to software-only emulation without KVM
   • SeaBIOS: open source implementation of a 16-bit x86 BIOS
3. libvirt: open source API for platform virtualization (daemon and mgmt tool)
   • manages KVM, QEMU (Xen, VMware ESX…)
4. virsh: command line interface tool for managing guests and the hypervisor
   • built on libvirt

 <disk type='file' device='cdrom'>
      <driver name='qemu' type='raw'/>
      <source file='/iso/CentOS-7.0-1406-x86_64-livecd.iso'/>
      <target dev='hdd'/>
      <readonly/>
 </disk>

<os>
    <boot dev='cdrom'/>
    <boot dev='hd'/>
    <bootmenu enable='yes'/>
</os>

virsh attach-disk domain1 /iso/CentOS-7.0-1406-x86_64-livecd.iso hdc --type cdrom --mode readonly