<div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div class="gmail_quote"><div><br></div><div>Second... Xen works differently than VMware or Virtualbox... both of those operate ON TOP of an OS.... hypervisors like Xen and HyperV operate below the OS... the DOM0 OS is only there to manage the hypervisor, it's actually virtualized itself.</div>
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</blockquote></div><br><div>For clearification see:</div><div><br></div><div><a href="http://en.wikipedia.org/wiki/Hypervisor">http://en.wikipedia.org/wiki/Hypervisor</a></div><div><br></div><div><p style="margin:0.4em 0px 0.5em;line-height:19.200000762939453px;font-family:sans-serif;font-size:13px;background-color:rgb(255,255,255)">
Robert P. Goldberg classifies two types of hypervisor:<sup id="cite_ref-4" class="reference" style="line-height:1em"><a href="http://en.wikipedia.org/wiki/Hypervisor#cite_note-4" style="text-decoration:none;color:rgb(11,0,128);background-image:none;white-space:nowrap;background-repeat:initial initial">[5]</a></sup></p>
<ul style="line-height:19.200000762939453px;list-style-type:square;margin:0.3em 0px 0px 1.6em;padding:0px;font-family:sans-serif;font-size:13px;background-color:rgb(255,255,255)"><li style="margin-bottom:0.1em"><i>Type 1</i> (or <i>native</i>, <a href="http://en.wikipedia.org/wiki/Bare_metal" title="Bare metal" class="mw-redirect" style="text-decoration:none;color:rgb(11,0,128);background-image:none;background-repeat:initial initial">bare metal</a>) hypervisors run directly on the host's hardware to control the hardware and to manage guest operating systems. A guest operating system thus runs on another level above the hypervisor.</li>
</ul><dl style="margin-top:0.2em;margin-bottom:0.5em;font-family:sans-serif;font-size:13px;line-height:19.200000762939453px;background-color:rgb(255,255,255)"><dd style="line-height:1.5em;margin-left:1.6em;margin-bottom:0.1em;margin-right:0px">
This model represents the classic implementation of virtual machine architectures; the original hypervisors were the test tool, <a href="http://en.wikipedia.org/wiki/SIMMON" title="SIMMON" style="text-decoration:none;color:rgb(11,0,128);background-image:none;background-repeat:initial initial">SIMMON</a>, and <a href="http://en.wikipedia.org/wiki/CP/CMS" title="CP/CMS" style="text-decoration:none;color:rgb(11,0,128);background-image:none;background-repeat:initial initial">CP/CMS</a>, both developed at <a href="http://en.wikipedia.org/wiki/IBM" title="IBM" style="text-decoration:none;color:rgb(11,0,128);background-image:none;background-repeat:initial initial">IBM</a> in the 1960s. CP/CMS was the ancestor of IBM's <a href="http://en.wikipedia.org/wiki/Z/VM" title="Z/VM" style="text-decoration:none;color:rgb(11,0,128);background-image:none;background-repeat:initial initial">z/VM</a>. Modern equivalents of this are <a href="http://en.wikipedia.org/wiki/Logical_Domains" title="Logical Domains" style="text-decoration:none;color:rgb(11,0,128);background-image:none;background-repeat:initial initial">Oracle VM Server for SPARC</a>, the Citrix <a href="http://en.wikipedia.org/wiki/Xen" title="Xen" style="text-decoration:none;color:rgb(11,0,128);background-image:none;background-repeat:initial initial">XenServer</a>, <a href="http://en.wikipedia.org/wiki/Kernel-based_Virtual_Machine" title="Kernel-based Virtual Machine" style="text-decoration:none;color:rgb(11,0,128);background-image:none;background-repeat:initial initial">KVM</a>, <a href="http://en.wikipedia.org/wiki/VMware_ESX" title="VMware ESX" style="text-decoration:none;color:rgb(11,0,128);background-image:none;background-repeat:initial initial">VMware ESX</a>/ESXi, and Microsoft <a href="http://en.wikipedia.org/wiki/Hyper-V" title="Hyper-V" style="text-decoration:none;color:rgb(11,0,128);background-image:none;background-repeat:initial initial">Hyper-V</a> hypervisor.</dd>
</dl><ul style="line-height:19.200000762939453px;list-style-type:square;margin:0.3em 0px 0px 1.6em;padding:0px;font-family:sans-serif;font-size:13px;background-color:rgb(255,255,255)"><li style="margin-bottom:0.1em"><i>Type 2</i> (or <i>hosted</i>) hypervisors run within a conventional <a href="http://en.wikipedia.org/wiki/Operating_system" title="Operating system" style="text-decoration:none;color:rgb(11,0,128);background-image:none;background-repeat:initial initial">operating system</a> environment. With the hypervisor layer as a distinct second software level, guest operating systems run at the third level above the hardware. <a href="http://en.wikipedia.org/w/index.php?title=BHyVe&action=edit&redlink=1" class="new" title="BHyVe (page does not exist)" style="text-decoration:none;color:rgb(165,88,88);background-image:none;background-repeat:initial initial">BHyVe</a>, <a href="http://en.wikipedia.org/wiki/VMware_Workstation" title="VMware Workstation" style="text-decoration:none;color:rgb(11,0,128);background-image:none;background-repeat:initial initial">VMware Workstation</a> and <a href="http://en.wikipedia.org/wiki/VirtualBox" title="VirtualBox" style="text-decoration:none;color:rgb(11,0,128);background-image:none;background-repeat:initial initial">VirtualBox</a> are examples of Type 2 hypervisors.</li>
</ul></div><div><br></div><div><a href="http://wiki.xen.org/wiki/Xen_Overview">http://wiki.xen.org/wiki/Xen_Overview</a></div><div><br></div><div><span style="font-family:sans-serif;font-size:13px;line-height:19.03333282470703px;background-color:rgb(255,255,255)">Xen is an open-source </span><a href="http://en.wikipedia.org/wiki/Hypervisor" class="extiw" title="wikipedia:Hypervisor" style="text-decoration:none;color:rgb(51,102,187);background-image:none;background-color:rgb(255,255,255);padding:0px;font-family:sans-serif;font-size:13px;line-height:19.03333282470703px">type-1 or baremetal hypervisor</a><span style="font-family:sans-serif;font-size:13px;line-height:19.03333282470703px;background-color:rgb(255,255,255)">...</span></div>