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What are the differences between an exokernel operating system and a virtual machine kernel (hyper visor) or a virtual language run time like JVM?

zeitue wrote:can also run as a virtual machine hosted on another OS

I have been reading about AROS, especially the hosted version. AROS says the following.

kernel.resource contains AROS microkernel. It's the lowest level component,
which is responsible for handling CPU and motherboard. For
hosted ports kernel.resource contains a virtual machine.

From what I have read about virtual machines is that there are 2 types system virtual machines and process virtual machines. I know that AROS is not a system virtual machine, but all the process virtual machines seam to be like Java JVM, Mono, Python, Ruby, etc. They all seam to be language specific. Where as AROS seams to be a complete system/platform running in user mode kind of like User Mode Linux.

AROS-hosted: An Operating System in an Operating System?

AROS is originally developed on Linux running on an Intel-based computer. It runs on many more machines and operating systems, though. This may sound strange: an OS running on top of an other OS, that's emulation, right?

A nice term for what AROS-hosted does is "API emulation". API is a three-letter acronym for Application Programmer's Interface. In plain English: an API provides (C Language) functions that a programmer can use. The AmigaOS API consists of a load of library calls that an Amiga programmer can use to make an Amiga program. AROS emulates the AmigaOS API: it tries to provide the same library calls as AmigaOS. An Amiga emulator, such as UAE; emulates the Amiga computer: the processor, the connected hardware, everything. This has its advantages, like being able to play binary Amiga games on different hardware, and its disadvantages, like not being able to use the emulator as a "real" OS, on a "real" processor. AROS-hosted runs on the "real" processor. But it isn't a "real" OS, unless you run in such a way that it doesn't require Linux. This is called "native" AROS.

AROS can run natively on the Intel and Amiga computers, but not quite as well as it runs on Linux. AROS library functions are made to run under Linux first, internally using Linux kernel and library calls. This way a programmer has the opportunity to bother about the implementation of the whole system first, and to bother about the technical details in a later stadium. People are currently working on making the "native" AROS more usable. The results are very impressive and it is perfectly possible to use AROS-native as a real (and only) Operating system on an IBM PC compatible machine.

Of course, AROS is not only an API emulator. It also tries to provide replacements to all the AmigaOS 3.1 system software, and you will also find a few demo's and games being shipped with AROS, just to show that they work - we might just be at 77% of the whole system, but we already have Quake running!