On Wed, Sep 2, 2020 at 9:50 AM ZB wrote:
>
> If I'm correct, Dosemu uses "virtual x86 mode" of 386 and later processors.
> But Dosemu of course needs "host OS".
>
> I wonder does there exist any utility that offers "virtual x86 mode" and
> acts as "host" by itself? Suppose we have (quite modest for today) computer
> with 386/486 and 4 MB RAM. Theoretically it should be possible to run quite
> comfortably four DOS "instances" each one having 1 MB just for itself - and,
> say, switching among them with - like among consoles in Linux.
What you are talking about are full blown Virtual Machine setups. The
VM sits between the host machine's hardware and the OS to be
virtualized. Examples in the commercial software world include things
like VMWare, and in the open source world we have Oracle's Virtual
Box. For that matter, Microsoft has a virtual machine setup,
specialized for running more than one Windows instance. With a full
VM, the *OS* can be virtualized as well as the applications running
under the OS, because the "hypervisor" sits between the OSes and the
hardware.
I used VMWare at a former employer. We were a streaming video
provider. Our preferred servers were 1u Dell rackmount units with
dual 3ghz Xeon CPUs and 32GB RAM. Servers under VMWare were running
CentOS, the open source flavor of Red Hat Enterprise Linux. (Linux is
open source, and you can get the code free. What Read Hat sold was
*support*.) Spinning up a new server under VMWare was a trivial
exercise. (Depending on the OS. A co-worker had a *lot* of fun
trying to spin up a virtualized WinXP instance...) We had load
balancing on traffic coming into the servers, so requests got routed
to whichever running server had the capacity. (And what we did did
not require maintaining state and history, so new incoming requests
could go to whichever server happened to be available.)
The concept is an old one. I worked at a bank that was an IBM
mainframe shop in the 80s. IBM had a virtual machine OS called
VM/CMS. You could load other IBM mainframe OSes under it, and it
imposed about 10% overhead. A popular use case was a shop currently
running IBM's DOS/VSE OS who wanted to migrate to OS/MVS. Making the
move was non-trivial. There were all manner of changes you needed to
make to your workflow and your applications to do this. So you ran
VM/CMS, brought DOS/VSE up under it in a production partition, and
OS/MVS in a test partition. Normal workloads connected to the DOS/VSE
instance. Applications being migrated and tested to make sure they
ran as designed were in the test partition. Once migration was
completed and fully tested to confirm everything worked correctly,
DOS/VSE could be taken down and OS/MVS became the production
environment.
But as you might guess, you need a powerful machine to be able to
support this usage, and server class machines generally have hardware
designed to make it easy to run a VM. The goal is maximizing hardware
usage. I went through that exercise at another employer with lots of
dedicated servers for different purposes, some of which were barely
used. Instead of adding more and more servers (which required more
and more power and cooling) install VMWare and consolidate. It got
nowhere because a British sister company had tried to do that and
failed. I thought they simply didn't know what they were doing and we
*could* do it, but the decision not to was made several levels above
me.
> So concentrating on using DOS - because 486 is much too "weak" for Linux of
> today - I mean utility whose duty is just to switch CPU into "virtual x86
> mode", split RAM among established "instances" and then just share hardware
> resources (keyboard, CD-ROM, video, sound... everything) among them.
Just what do you mean when you say 486? They came in a variety of
makes/models. A 486 *can* run Linux, with reasonable performance
depending on what you want to do.. Mostly, you want to give it as much
RAM as the machine can accommodate. Linux distros exist intended for
older, less powerful hardware.
You *might* be able to configure a Linux instance on that hardware
that would let you multi-boot using Grub2 or the like, and pick which
flavor of DOS you wanted to run that session. You almost certainly
*won't* be able to have multiple different instances of DOS running
simultaneously.
> No idea - maybe it had been aleady created, just I didn't stumble upon it yet?
It doesn't exist. See above for why.
> regards,
> Zbigniew
__
Dennis
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