Re: [Freedos-devel] DOS Development Idea

[Eric A. <e....@jp...>]

Hi!

> 	Is there a list of applications, currently available for DOS
> 	only, that it may make sense to reimplement for contemporary
> 	free software systems?
> 
> 	For me, it's probably only certain games.  (In particular, those
> 	still distributed via http://gog.com/.)

There are usually no source codes available for classic DOS games.
Also, as mentioned earlier, DOS has very low hardware requirements
and even some new software just runs better when there is no big
"contemporary OS" running in the background, eating CPU time, or
interfering with direct hardware access.

>  > Like it or not, the path for the future is going to be running DOS
>  > inside of virtual machines hosted by an operating system that...

Well for certain drivers, that makes sense, in particular
given that classic DOS software often comes without source
code so you cannot update their drivers, e.g. for sound.

Alternatively, you could write a driver for DOS which will
provide only a virtual soundcard and send the sound to the
actually AC97 or HDA soundchip of your modern PC.

Similar: USB joysticks, WLAN and UMTS networking. Other USB
devices (keyboard, mouse, printer, serial port) might work
with DOS drivers which only provide BIOS like services, as
even in DOS, software can use the BIOS to access those and
does not have to use direct I/O for which a virtualization
driver would be required to use...

>  > that we are going to need.  Virtual environments are going to look
>  > pretty attractive when you can't boot a machine with DOS running on
>  > the bare metal in a few years.

Yet I do still think that you can load "classic BIOS"
functionality as a module for your EFI BIOS, or use a
part of a boot menu to do so, even in the future. Note
that some hardware might require "signed" software but
on such possibly "Win8/WinPhone tablet or smartphone"
style hardware, even Linux will need tricks to boot...

> 	So, the only use of DOS nowadays is to provide a compatibility
> 	layer on top of a “proper” system.
> 
> 	Which makes me wonder, are there any efforts being made to allow
> 	FreeDOS make use of Xen's paravirtualization?

DOS itself not much, but remember that modern VM like
VMware or VirtualBox can use really advanced things,
even "hypervisor style" CPU functions or on the fly
recompilation / rewriting of your apps, to gain speed.

> 	Formely, DOSEMU provided a kind of paravirtualization, but as
> 	the Virtual 8086 mode slowly moves into the oblivion, it makes
> 	little sense to continue with DOSEMU development.  (Which I see
> 	has ceased by now.  QEMU, including instances that use hardware
> 	virtualization via Linux' KVM, provide a nice alternative, ...

What makes you think that dosemu development has ceased?
The dosemu mailing list is quite active, although not so
many people post there - two of the big experts mainly,
and occasionally somebody who suggests a patch or reports
a bug, for example :-)

You may also want to look at the v86-64 patch on sourceforge
which makes it possible to use vm8086 mode even on a 64 bit
Linux host OS, by switching modes more aggressively. This is
of course slower than directly having vm86 tasks on a 32 bit
Linux, and may interfere with Linux driver speeds, but it is
a possible solution :-) Not yet part of any mainstream Linux
kernel, but I think since some maintainers / policies there
have changed, some lobbying might be able to change that :-)

Before, the patch was not able to go mainstream at all. Note
that the patch is a few years old, but 64 bit CPU still have
the same specs regarding the vm86 topic so it is still up to
date if you ask me :-)

http://v86-64.sourceforge.net/
http://sourceforge.net/projects/v86-64/files/

Eric