[Oberon] Oberon V4 on the Raspberry Pi?

Liam Proven lproven at gmail.com
Mon Jan 11 16:29:04 CET 2021

On Mon, 11 Jan 2021 at 16:13, Joerg <joerg.straube at iaeth.ch> wrote:
> Today, this is also called "virtualization" with a HostOS and a GuestOS (=Oberon System)

Not the same thing.

Full-system virtualisation, that is a hypervisor such as KVM, Xen,
VMware or VirtualBox, basically means an emulator that emulates an
entire computer _on the same computer architecture_.

This is a built-in feature of SPARC, IBM POWER etc. It was not a
feature of x86 until Intel added its VT feature (and AMD its AMD-V)
around 2005-2006. This adds a "ring -1" underneath Ring 0, the
"supervisor mode" of traditional x86.

Linux' KVM uses the VT/AMD-D feature and cannot work without it.
Similarly, Microsoft's Hyper-V does the same.

But Hyper-V evolved from a program called Virtual PC, which is still a
free download from MS:

MS acquired Virtual PC when it acquired Mac vendor Connectix.
VirtualPC originated as a Mac software emulator allowing you to run PC
OSes as programs under Classic MacOS on PowerPC processors.

In other words, a hypervisor is just a special case of an emulator: it
emulates a platform _on the same platform_.

But inside a hypervisor's VM, you have a whole empty PC complete with
emulated BIOS, emulated disks, emulated RAM, emulated graphics card,
emulated network interface, etc.

Oberon runs like this, sure. But so can any PC OS.

Oberon _also_ runs as a program on top of other OSes. For example here
is a Mac version:

This is an emulator, not a VM. It emulates a RISC5 computer, in a
resizable window.

It also runs _as a program_ on top of Windows, Linux and macOS.
Downloads are here:

This does not use a hypervisor or a VM. This is the OS built as a
program to run on top of another OS.

A closer comparison is User Mode Linux on top of another Linux distro:

Or CoLinux on Windows:

To the host OS, these are not VMs, they are programs. But the
"program" is an OS and to apps inside the program, they are running on
their own system, not on the host OS.

So I am not saying you are _wrong_ -- I am saying _both_ are true.
There is a version for hypervisors, that runs in a VM, *and* there are
native versions that run on Windows, Linux and macOS. They are
different entities. The hosted versions can't run in a VM, and the
bare-metal version will not execute under another OS.

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