Re: [ros-dev] (Free)DOS subsystem

[Imre Leber]

>  -----Original Message-----
> From: Peter Dolding [mailto:[e-mail]]
> Sent: Tuesday, August 29, 2006 01:33 PM
> To: 'ReactOS Development List'
> Subject: Re: [ros-dev] (Free)DOS subsystem
>
> Myria wrote:
> >   I've wanted to write an NTVDM for ReactOS,
> > but I'm not sure when I'd ever 
> >  have time.
> >
> >  Windows NT's DOS subsystem, NTVDM, is a user-mode program that runs on top 
> >  of Win32.  It runs DOS programs as Windows processes, using v86 mode to run 
> >  the programs.  DPMI programs are supported by asking the kernel to allocate 
> >  LDT segments and running directly.  (If you write a DOS32 program and know 
> >  the correct addresses, you can call MessageBoxW in user32.dll and it will 
> >  work.)
> >
> >  This differs significantly from DOSBox, which is effectively a machine 
> >  emulator rather than an API translator.  DOSEmu, in comparison, is 
> >  essentially the same design as NTVDM but for Linux.
> >
> >  FreeDOS in DOSBox works very well, because the FreeDOS kernel is its normal 
> >  self and is unaware that it's inside a VM.  However, this doesn't work for 
> >  NTVDM/DOSEmu.  In these, the FreeDOS kernel will need to be heavily 
> >  modified, particularly because the NT kernel handles file I/O.  Programs 
> >  inside the virtual DOS environment use illegal opcodes to talk to NTVDM.
> >
> >  Melissa
> >     
> True  Closest Freedos to Windows NT NTVDM is 
> http://freedos-32.sourceforge.net/.   Its was newer version under 
> development.  It could be stalled from 2005.
>  
Why?

I never got it. It doesn't seem to add anything new. Nothing that can't be done in
FreeDOS.

FreeDOS is for all pratical purposes a capable 32 bit system. It can run 32 bit DOS and
(some) windows programs and it has multithreading (eRTOS), TCP/IP (watt32), etc... . 

I think it would not be very difficult to write a multitasking DOS extender either (maybe
as an extension to cwsdpr0).

If it's because it is running in 32 bit, I am not all that convinced that DOS-C can
not be ported to 32 bit. It was originally intended to run on apple macintosh.

Imre

>  Peter Dolding
>
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