On Wed, Sep 2, 2020 at 9:50 AM ZB <[email protected]> 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 <Alt>-<F-key> 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 _______________________________________________ Freedos-user mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/freedos-user
