On Wednesday 20 January 2010 11:45:32 Sthu Deus wrote: > Thank You for Your time and answer, Boyd: > >Xen also supports running unmodified guest OSes. > > Excuse me, but what does it mean "unmodified guest OS"? A guest OS that hasn't been modified to support whatever virtualization technology you are currently discussing. VServer and OpenVZ requires the guests to know they are running in a virtualized environment, since they share a kernel with the host. They don't support unmodified guest OSes. Xen originally also had this requirement, although the kernels were separate, there were specific Xen calls a guest would need to use instead of processor- native instructions. This was before VT was in virtually every desktop- and server-class processor. Supposedly, Xen supported an MS Windows guest at the time, but it was modified through a binary patch system and could not be released. Once VT came around, this requirement soon was dropped from Xen. Using the VT extensions in the host, you could have the host handle the processor-native instructions being executed by a guest through a trap system. This meant that Xen could support unmodified guest OSes, at least on systems that support VT. I'm not even sure if modern Xen will work without VT extensions. Qemu and friends originally did full emulation. This allows unmodified guest OSes from day 1, but it is rather slow, even in a best-case scenario. KQemu allowed the emulated MMU to be mapped onto the actual MMU of the system, which made things much faster. The KVM kernel module does that, and more, through the use of the VT extensions. -- Boyd Stephen Smith Jr. ,= ,-_-. =. bss@iguanasuicide.net ((_/)o o(\_)) ICQ: 514984 YM/AIM: DaTwinkDaddy `-'(. .)`-' http://iguanasuicide.net/ \_/
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