KQEMU 1.3.0pre10 released - under the GPL
Posted Feb 8, 2007 13:27 UTC (Thu) by drag
In reply to: KQEMU 1.3.0pre10 released - under the GPL
Parent article: KQEMU 1.3.0pre10 released - under the GPL
I wrote something a while ago. Keep in mind that I am very amature at this sort of thing. http://aplawrence.com/Linux/kvm_virtualization.html
Pretty innaccurate, but I suppose you can get my meanings by my descriptions. I know more about this stuff now.
Basicly you have hypervisors, VM-as-a-application, containers, and emulation. All these things overlap to one degree or another and it's very difficult to put some things into nice catagories.
But generally speaking you have hypervisors. Examples are going to be like Xen or Vmware ESX. These things are specialized kernel-like things that are specially designed to create VMs. Then in addition you'll have a userland based on a OS to manage and provide I/O emulation. Both of these things use Linux for that to one extent to another.
These provide the highest level of sophistication, isolation, and management options and generally have the best performance of a VM capable of running different sorts of operating systems. The most 'Enterprise'ish.
Then you have VM-as-a-application stuff. Like Qemu, or Vmware's Server/Workstation/player stuff. These things are more convient, but are subject heavily to the performance limitations of the host OS combined with the performance limiations of the hosted OS along with some emulation overhead. Not the fastest, but not the slowest either. Offer good-enough performance for the majority of tasks you'd want to do in a VM.
Something like KVM actually turns the Linux kernel into a hypervisor, but in practice it seems more like the second catagory.
Then you have container-type things. Like Vserver, or OpenVZ. Think about those things as 'chroot on steroids'. They share the same kernel and work about the same as a chroot, but are designed for much higher security and isolation then what is normally possible. Since there is no software vm or emulation of anything going on these provide the highest performance and most efficient use of resources. Much better then anything else. The downside is that a kernel exploit can open up all your VM's.. and you can't run anything that is not the same as the host OS.
Then you have something like Usermode Linux. It's sort of like Vserver, but is more like a real VM. You can't run anything like Windows in it, but it does provide higher level of isolation and such.
Then you have emulation. Bochs is the best example I can think of. It's a full-on computer-expressed-in-software. Everything is in software. Software sound card, software video card, software cpu, etc etc. The whole ten yards. With this you can run x86 code on Sparc or PowerPC or anything else, it's full software. It's also very slow.
For a more expert overview check out:
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