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I have a general question about Virtual Machines.
It is not clear to me if I need an operating system at the lower level and then install the VM and on top of that the rest or I can install a VM without any OS present.
Could someone clarify?

Jim
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  • https://en.wikipedia.org/wiki/Hypervisor – Michael Hampton Sep 28 '21 at 21:12
  • @MichaelHampton: Based on the wiki if the VM has a type-1 hypervisor it runs directly on HW? Is the hypervisor an OS? – Jim Sep 28 '21 at 21:25
  • That is answered in the wikipedia article already. – Michael Hampton Sep 28 '21 at 21:29
  • @MichaelHampton: I am not sure if the wiki is purely theoretical. The way it is phrased there sounds like a theoretical clasification but not what actually implementations offer. At least this is what I get from the sentence mentioning KVMs. that convert the hostOS to something else.Am I misunderstanding this? – Jim Sep 28 '21 at 21:35
  • No, you actually understood that bit correctly. There is a long standing argument about whether KVM on Linux is a type 1 or type 2 hypervisor. In practice it doesn't matter much. – Michael Hampton Sep 28 '21 at 21:38

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A VM is, by definition, an operating system running inside an operating system. So no, you can't run a VM directly on hardware.

There are always exceptions to rules, and a VM with a VHD for a disk is kind of one. Windows allows you to boot from a VHD file. But none of the settings of the VM (RAM, network configuration, other storage configuration, etc.) are used, and the guest OS inside the VHD has to support the hardware directly instead of the virtual hardware typically provided by the hypervisor.

longneck
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  • What is a "VHD"? – Jim Sep 28 '21 at 19:25
  • So what is meant with Hardware virtualization then? – Jim Sep 28 '21 at 19:39
  • "Hardware virtualization" is an ambiguous term. It could mean one of many different things, none of which allow "install a VM without any OS present". – longneck Sep 28 '21 at 20:34
  • A VHD is a "Virtual Hard Disk", a Microsoft file format for virtualizing a hard drive for a VM. – longneck Sep 28 '21 at 20:34
  • how about as phrased here? https://www.vmware.com/topics/glossary/content/virtual-machine Is that some specific kind of VM? – Jim Sep 28 '21 at 20:44
  • Does hypervisor that you also mention run on top of the OS or interacts with hw drivers directly? – Jim Sep 28 '21 at 20:45
  • Is hypervisor an OS or does it run on top of the OS? – Jim Sep 28 '21 at 20:56
  • The hypervisor is the software that allows a computer to run virtual machines. vmware (the kind that runs on servers) and Hyper-V are examples of "hardware virtualization" in that page you linked to. In over-simplified terms, the hypervisor is what actually runs directly on the hardware. The "host" operating system runs as a specially privileged "guest" on top of the hypervisor, and gets direct access to the hardware. Guests use virtual hardware provided by the hypervisor, or direct access to hardware via hypervisor-specific drivers. https://nativebyte.co/images/header/virtualisation1.png – longneck Sep 29 '21 at 00:07