Re: Found something interesting re MS-DOS

From: Spiro Trikaliotis <ml-cbmhackers_at_trikaliotis.net>
Date: Thu, 4 Jan 2018 22:42:35 +0100
Message-ID: <20180104214235.GA7433@hermes.local.trikaliotis.net>
Hello,

* On Thu, Jan 04, 2018 at 09:42:15PM +0100 silverdr@wfmh.org.pl wrote:
> 
> > On 2018-01-04, at 21:34, Michał Pleban <lists@michau.name> wrote:
> > 
> > silverdr@wfmh.org.pl wrote:
> > 
> >> AFAIR except those from Microsoft, which detect the "incompatible" environment and show its middle finger to the user ;-) Or something like that...
> > 
> > It was Windows, and only the beta version. It is documented in detail in
> > "The undocumented DOS" which I gave Ruud to scan.
> 
> Memory may not serve well but I recall this from around 84 or so.

Windows 3.1 in 1984? For sure not. ;)


A discussion of this topic from the Microsoft side can be found here:

https://blogs.msdn.microsoft.com/larryosterman/2004/08/13/so-why-didnt-the-windows-guys-just-remove-the-aard-code-from-the-system/

and 

https://blogs.msdn.microsoft.com/larryosterman/2004/08/12/aardvarks-in-your-code/

Money quote:

   "In order to get Windows to work, I had to change the DOS loader to
   detect when win.com was being loaded, and if it was being loaded, I
   looked at the code at an offset relative to the base code segment,
   and if it was a “MOV” instruction, and the amount being moved was the
   old size of the SFT, I patched the instruction in memory to reflect
   the new size of the SFT!  Yup, MS-DOS 4.0 patched the running windows
   binary to make sure Windows would still continue to work."


The technical discussion of the code can be found here:

http://collaboration.cmc.ec.gc.ca/science/rpn/biblio/ddj/Website/articles/DDJ/1993/9309/9309d/9309d.htm


Regards,
Spiro.

-- 
Spiro R. Trikaliotis
http://www.trikaliotis.net/

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