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From: Lawrence D'Oliveiro <ldo@nz.invalid>
Newsgroups: comp.os.vms
Subject: Re: VMWARE/ESXi Linux
Date: Tue, 3 Dec 2024 20:27:48 -0000 (UTC)
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On Tue, 3 Dec 2024 09:57:31 -0500, Arne Vajhøj wrote:

> I think the relevant distinction is that type 1 runs in the kernel while
> type 2 runs on the kernel.

<https://en.wikipedia.org/wiki/Hypervisor>:

    Type-1, native or bare-metal hypervisors
        These hypervisors run directly on the host's hardware to
        control the hardware and to manage guest operating systems.
        For this reason, they are sometimes called bare-metal
        hypervisors. The first hypervisors, which IBM developed in the
        1960s, were native hypervisors.[8] These included the test
        software SIMMON and the CP/CMS operating system, the
        predecessor of IBM's VM family of virtual machine operating
        systems. Examples of Type-1 hypervisor include Hyper-V, Xen
        and VMware ESXi.

    Type-2 or hosted hypervisors
        These hypervisors run on a conventional operating system (OS)
        just as other computer programs do. A virtual machine monitor
        runs as a process on the host, such as VirtualBox. Type-2
        hypervisors abstract guest operating systems from the host
        operating system, effectively creating an isolated system that
        can be interacted with by the host. Examples of Type-2
        hypervisor include VirtualBox and VMware Workstation.

    The distinction between these two types is not always clear. For
    instance, KVM and bhyve are kernel modules[9] that effectively
    convert the host operating system to a type-1 hypervisor.[10]

I would say those examples contradict the definitions, since Linux with 
KVM is very much a “conventional OS”, and the same would be true of the 
BSDs.

But then again, that just reinforces the point that the distinction is 
obsolete.