From: commodorejohn@gmail.com   
      
   On Mon, 10 Mar 2025 23:11:49 -0000 (UTC)   
   cross@spitfire.i.gajendra.net (Dan Cross) wrote:   
      
   > I already posted the definition I like to use, which came to me   
   > via Mothy Roscoe, at ETH, but I'll post it again:   
   >   
   > He defines the operating system as,   
   > That body of software that,   
   > 1. Multiplexes the machine's hardware resources   
   > 2. Abstracts the hardware platform   
   > 3. Protects software principles from each other   
   >    (using the hardware)   
      
   You surely did; however, that does not mean that anybody else is   
   obligated to accept it. Specifically, let me ask:   
      
   1. Why must it multiplex anything, in a single-user system? Multi-   
      tasking is certainly a nicety, but why should it be considered   
      a necessary criterion for "real" status?   
   2. What is the minimum level of hardware abstraction, and why? MS-DOS   
      does in fact abstract the details of, e.g., filesystem access, pipes,   
      and to a lesser extent serial/parallel communications. You seem to be   
      fixated on the fact that its ABI uses x86 interrupts rather than an   
      alternative method; why is this important?   
   3. Again, in an 8086 environment this is *literally impossible.* There   
      is no operating system for the IBM PC or XT that *can* implement any   
      kind of protection. Additionally, in a single-user system, why is   
      this a requirement rather than a nicety?   
      
   > >MS-DOS very definitely takes control of the computer - it does not   
   > >*hold onto it* very tightly, but there's no particular reason it   
   > >should have to.   
   >   
   > Given the above definition, there's a very good reason: how does   
   > it otherwise protect _itself_, as a software principle, from an   
   > errant, let alone malicious, program?   
      
   It doesn't, because it cannot. The 8086 offers absolutely no facility   
   for protection, nor does the PC hardware implement any kind of bolt-on   
   mechanism for this. That did not even become *possible* until the   
   introduction of the PC/AT in 1984, three years after DOS was released,   
   and that was limited by the infamously "brain-damaged" protected mode of   
   the 286.   
      
   > Also, a boot loader takes control of the computer, albeit   
   > temporarily: is that also an operating system?  Merely taking   
   > control of the computer is insufficient.  The OpenBoot PROM   
   > monitor on a SPARCstation could be entered via a keyboard   
   > shortcut, suspending Unix and the SPARC processor; was that an   
   > "operating system"?   
      
   In the strict sense, I don't see why not. A primitive one, granted, but   
   if ROM BASIC counts as an operating system, OpenBoot certainly would.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)