From: cross@spitfire.i.gajendra.net   
      
   In article ,   
   Scott Lurndal  wrote:   
   >cross@spitfire.i.gajendra.net (Dan Cross) writes:   
   >>In article <87o6ybbeqw.fsf@example.com>,   
   >>Salvador Mirzo   wrote:   
   >>>scott@slp53.sl.home (Scott Lurndal) writes:   
   >>>> MS-DOS is, was, and always will be a toy.  It's not even   
   >>>> a real operating system.   
   >>>   
   >>>And why is that?  Is it mainly because it doesn't time-share the CPU?   
   >>   
   >>It depends on your definition of an operating system, I suppose.   
   >>I like the definition Mothy Roscoe (ETH) used in his OSDI'21   
   >>keynote:   
   >>   
   >>The operating system is that body of software that:   
   >>1. Multiplexes the machine's hardware resources   
   >>2. Abstracts the hardware platform   
   >>3. Protects software princples from each other   
   >>   (using the hardare)   
   >>   
   >>It's hard to see how MS-DOS fits that definition in a meaningful   
   >>way.  Does it multiplex the machine's hardware resources?  Well,   
   >>no; not really.  While it does provide a primitive filesystem,   
   >>and exposes some interface for memory management, it only lets   
   >>one program run at a time, and that program doesn't have to use   
   >>or honor DOS's filesystem or memory management stuff.   
   >   
   >To partially aleviate these defects, a concept called TSR (Terminate and   
   >Stay Resident) was developed for MS-DOS.   However, conflicts   
   >between various TSRs were endemic and there was no hardware   
   >protection between them or between them and the application   
   >code.   
   >   
   >https://en.wikipedia.org/wiki/Terminate-and-stay-resident_program#Faults   
      
   Oh gee, as a form of mental self-protection, I had blanked that   
   madness out of my mind.  What an awful interface.  I do hand it   
   to people who were writing DOS programs; without any real form   
   or protection between programs, let along between DOS and   
   programs, it's amazing that anything there worked at all.   
      
   Still, lack of multiprogramming shows that they were targetting   
   an audience that was pretty unsophisticated.  I get that the   
   hardware was limited, but Unix on the PDP-7 supported multiple   
   users in 8KiW of 18-bit memory in 1969.  A 16-bit system 12   
   years later could have supported a real OS, albeit without   
   useful memory protection (CPU rings and the CPL didn't show up   
   until the 80286).  I suppose one could have played games with   
   segmentation to isolate a small kernel; as I understand it,   
   that was how the various Unix ports worked.  It's weird to me   
   how the 8086 included support for multiprocessing systems, but   
   not a mode bit for a kernel.   
      
   It's fun to speculate how the world could have been different:   
   had Intel chosen the 68000 for the IBM PC, I imagine we could   
   have had much more reasonable software rather quickly.  The   
   ripple effects of the legacy of DOS and the 8086 are   
   unfortunate, at best.  Oh well.   
      
   	- Dan C.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)