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Re: z/PDOS-generic

From cross@spitfire.i.gajendra.net (Dan Cross)
Newsgroups alt.os.development
Subject Re: z/PDOS-generic
Date 2025-03-11 17:28 +0000
Organization PANIX Public Access Internet and UNIX, NYC
Message-ID <vqprsc$25q$1@reader1.panix.com> (permalink)
References <v7bbdt$2fj5a$1@dont-email.me> <20250310151114.000023e9@gmail.com> <vqnrjl$4a9$1@reader1.panix.com> <20250311083745.000076a4@gmail.com>

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In article <20250311083745.000076a4@gmail.com>,
John Ames  <commodorejohn@gmail.com> wrote:
>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.

Sure.  That's why I prefaced this entire subthread by saying,
"it depends on your definition."  I gave the definition that I
like, and explained how DOS does not meet those criteria.  Is
that unfair?  Perhaps, but the question was, "why do you say
this?" and that's the answer of why I say 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?

Note, I said multiplexing, not multitasking.  CPU is just one
hardware resource that can be multiplexed, often via
multiprogramming but sometimes via spatial allocation (e.g., in
a multiprocessor system).

But others include storage devices, memory, peripherals like
timers and other IO devices such as serial/parallel ports,
maybe a real-time clock, and so on.  You like having a file
abstraction?  Well, that's something that the OS often provides
for you, and is _a_ way that e.g. a storage device can be
logically multiplexed between multiple programs, even if they
do not run concurrently.  Similarly with a memory allocator.

Getting back to the specific example of MS-DOS, it does provide
both, but does Not provide a way to e.g., multiplex IO and
computation temporally; so performing a disk operation will
just block the program until the operation completes.  Don't
want that?  Go touch the hardware yourself.  The control program
doesn't really help me here.

>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?

I would hardly say I'm "fixated" on it.  It's simply a fact.

Generally, we draw a distinction between an API and ABI; the
former is often somewhat abstract, while the latter is the
concrete implementation of that abstraction.

In a lot of ways, the ABI is irrelevant for workaday
programming: you leave it up to a tool, or a system library, or
something like that, but you rarely have to think about it.  The
issue with the DOS API is that it is defined _solely_ in terms
of the hardware interface, and moreover it is highly specific to
that hardware.

Consider the memory allocation API, for example.  According to,
"Advanced MS-DOS Programming, 2nd Ed", by Ray Duncan, if a user
program wants to use expanded memory, the program must do work
to a) first determine whether expanded memory is even available,
and b) use a different, special, interrupt to delegate to the
"expanded memory manager" to actually allocate it.

Now, one might argue that this doesn't matter that much.  "Who
cares?  What's the difference between saying that there's a
thing called `malloc` and poking a hex constant into %ah and
then doing `int 0x67`?"  And that's a valid question; one could
imagine an interface that has both `malloc` and `expandedmalloc`
or something like that to have an API divorced from the specific
ABI, but those are _leaky abstractions_: they exist solely to
represent hardware artifacts.

So while you could "name" those things and not just number them,
the things themselves are still very tightly coupled to the
hardware.  Those aren't great abstractions.

>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?

Yup.  An 6802 microcontroller with 128 bytes of RAM doesn't have
an operating system, either.  That doesn't mean it isn't useful.

It's interesting that there was a port of Unix to the XT that
was, of course, subject to the same limitations.  Sometimes you
are just constrained, so you make due with what you have.  But
Unix at least used the segmentation facilities in the processor
to _attempt_ to shield the kernel from errant user processes;
DOS made no such attempt.

>> >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,

Not true.  It supported segmentation.  It's harder to corrupt
RAM if it's not in a segment that's currently addressible.

>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.

And when the 286 came out, MS-DOS didn't grow to use it, even
though it was there.  Nor did they try to incorporate larger
segments or virtual memory when the 386 came out.  But the 386
was designed for the Unix market, not the PC, so maybe MSFT gets
a pass on that one.

>> 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.

I wouldn't count ROM BASIC as an operating system, sorry.
Similarly, the people I know who worked on OpenBoot did not
consider it a real operating system in the way they thought of
SunOS.

Now my question to you: why do you care what specific label
people apply to MS-DOS?

	- Dan C.

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Thread

z/PDOS-generic "Paul Edwards" <mutazilah@gmail.com> - 2024-07-18 23:07 +0800
  Re: z/PDOS-generic Grant Taylor <gtaylor@tnetconsulting.net> - 2024-07-18 22:40 -0500
    Re: z/PDOS-generic "Paul Edwards" <mutazilah@gmail.com> - 2024-07-19 18:43 +0800
      Re: z/PDOS-generic scott@slp53.sl.home (Scott Lurndal) - 2024-07-19 16:18 +0000
        Re: z/PDOS-generic BGB-Alt <bohannonindustriesllc@gmail.com> - 2024-07-19 17:12 -0500
          Re: z/PDOS-generic scott@slp53.sl.home (Scott Lurndal) - 2024-07-19 23:21 +0000
            Re: z/PDOS-generic cross@spitfire.i.gajendra.net (Dan Cross) - 2024-07-19 23:31 +0000
            Re: z/PDOS-generic BGB <cr88192@gmail.com> - 2024-07-20 01:30 -0500
            Re: z/PDOS-generic John Ames <commodorejohn@gmail.com> - 2024-07-22 07:51 -0700
              Re: z/PDOS-generic cross@spitfire.i.gajendra.net (Dan Cross) - 2024-07-22 15:22 +0000
                Re: z/PDOS-generic John Ames <commodorejohn@gmail.com> - 2024-07-22 09:07 -0700
                Re: z/PDOS-generic cross@spitfire.i.gajendra.net (Dan Cross) - 2024-07-22 17:37 +0000
                Re: z/PDOS-generic scott@slp53.sl.home (Scott Lurndal) - 2024-07-22 18:07 +0000
                Re: z/PDOS-generic cross@spitfire.i.gajendra.net (Dan Cross) - 2024-07-22 19:38 +0000
                Re: z/PDOS-generic John Ames <commodorejohn@gmail.com> - 2024-07-22 11:18 -0700
              Re: z/PDOS-generic BGB <cr88192@gmail.com> - 2024-07-22 14:16 -0500
                Re: z/PDOS-generic scott@slp53.sl.home (Scott Lurndal) - 2024-07-22 20:14 +0000
                Re: z/PDOS-generic BGB <cr88192@gmail.com> - 2024-07-22 18:03 -0500
                Re: z/PDOS-generic scott@slp53.sl.home (Scott Lurndal) - 2024-07-22 23:58 +0000
                Re: z/PDOS-generic BGB <cr88192@gmail.com> - 2024-07-22 23:06 -0500
                Re: z/PDOS-generic "Paul Edwards" <mutazilah@gmail.com> - 2024-08-21 04:31 +0800
                Re: z/PDOS-generic BGB <cr88192@gmail.com> - 2024-08-28 02:28 -0500
                Re: z/PDOS-generic "Paul Edwards" <mutazilah@gmail.com> - 2024-08-28 16:54 +0800
                Re: z/PDOS-generic "Paul Edwards" <mutazilah@gmail.com> - 2024-08-28 16:58 +0800
                Re: z/PDOS-generic BGB <cr88192@gmail.com> - 2024-08-28 18:03 -0500
                Re: z/PDOS-generic "Paul Edwards" <mutazilah@gmail.com> - 2024-08-29 11:14 +0800
                Re: z/PDOS-generic George Neuner <gneuner2@comcast.net> - 2024-08-30 06:49 -0400
                Re: z/PDOS-generic George Neuner <gneuner2@comcast.net> - 2024-08-30 10:27 -0400
                Re: z/PDOS-generic "Paul Edwards" <mutazilah@gmail.com> - 2024-08-31 10:21 +0800
                Re: z/PDOS-generic George Neuner <gneuner2@comcast.net> - 2024-08-31 15:30 -0400
                Re: z/PDOS-generic cross@spitfire.i.gajendra.net (Dan Cross) - 2024-09-03 14:27 +0000
                Re: z/PDOS-generic wolfgang kern <nowhere@never.at> - 2024-08-30 13:29 +0200
          Re: z/PDOS-generic Waldek Hebisch <antispam@fricas.org> - 2024-09-03 23:38 +0000
            Re: z/PDOS-generic "Paul Edwards" <mutazilah@gmail.com> - 2024-09-06 07:46 +0800
              Re: z/PDOS-generic J. Curtis <unknown@protocol.invalid> - 2024-09-06 20:08 +0100
                Re: z/PDOS-generic "Paul Edwards" <mutazilah@gmail.com> - 2024-09-07 08:12 +0800
                Re: z/PDOS-generic "Paul Edwards" <mutazilah@gmail.com> - 2025-01-22 17:34 +1100
        Re: z/PDOS-generic J. Curtis <unknown@protocol.invalid> - 2024-07-20 00:02 +0100
        Re: z/PDOS-generic Salvador Mirzo <smirzo@example.com> - 2025-03-08 14:42 -0300
          Re: z/PDOS-generic cross@spitfire.i.gajendra.net (Dan Cross) - 2025-03-09 02:09 +0000
            Re: z/PDOS-generic scott@slp53.sl.home (Scott Lurndal) - 2025-03-09 15:40 +0000
              Re: z/PDOS-generic cross@spitfire.i.gajendra.net (Dan Cross) - 2025-03-10 12:38 +0000
                Re: z/PDOS-generic scott@slp53.sl.home (Scott Lurndal) - 2025-03-10 14:49 +0000
                Re: z/PDOS-generic cross@spitfire.i.gajendra.net (Dan Cross) - 2025-03-10 15:00 +0000
            Re: z/PDOS-generic Salvador Mirzo <smirzo@example.com> - 2025-03-10 09:21 -0300
              Re: z/PDOS-generic cross@spitfire.i.gajendra.net (Dan Cross) - 2025-03-10 13:50 +0000
                Re: z/PDOS-generic Salvador Mirzo <smirzo@example.com> - 2025-03-10 14:10 -0300
                Studying the system (was Re: z/PDOS-generic) cross@spitfire.i.gajendra.net (Dan Cross) - 2025-03-10 18:29 +0000
                Re: z/PDOS-generic "Paul Edwards" <mutazilah@gmail.com> - 2025-03-11 05:38 +1100
                Re: z/PDOS-generic scott@slp53.sl.home (Scott Lurndal) - 2025-03-10 19:07 +0000
                Re: z/PDOS-generic cross@spitfire.i.gajendra.net (Dan Cross) - 2025-03-10 19:09 +0000
                Re: z/PDOS-generic John Ames <commodorejohn@gmail.com> - 2025-03-10 13:00 -0700
                Re: z/PDOS-generic cross@spitfire.i.gajendra.net (Dan Cross) - 2025-03-10 20:20 +0000
                Re: z/PDOS-generic "Paul Edwards" <mutazilah@gmail.com> - 2025-03-11 07:59 +1100
                Re: z/PDOS-generic John Ames <commodorejohn@gmail.com> - 2025-03-10 15:11 -0700
                Re: z/PDOS-generic cross@spitfire.i.gajendra.net (Dan Cross) - 2025-03-10 23:11 +0000
                Re: z/PDOS-generic "Paul Edwards" <mutazilah@gmail.com> - 2025-03-11 10:51 +1100
                Re: z/PDOS-generic John Ames <commodorejohn@gmail.com> - 2025-03-11 08:37 -0700
                Re: z/PDOS-generic cross@spitfire.i.gajendra.net (Dan Cross) - 2025-03-11 17:28 +0000
                Re: z/PDOS-generic "Paul Edwards" <mutazilah@gmail.com> - 2025-03-12 05:40 +1100
                Re: z/PDOS-generic John Ames <commodorejohn@gmail.com> - 2025-03-11 12:41 -0700
                What is an operating system? (was Re: z/PDOS-generic) cross@spitfire.i.gajendra.net (Dan Cross) - 2025-03-11 21:00 +0000
                Re: What is an operating system? (was Re: z/PDOS-generic) "Paul Edwards" <mutazilah@gmail.com> - 2025-03-12 17:30 +1100
                Re: z/PDOS-generic John Ames <commodorejohn@gmail.com> - 2025-03-11 09:04 -0700
                Re: z/PDOS-generic "Paul Edwards" <mutazilah@gmail.com> - 2025-03-11 08:29 +1100
            Re: z/PDOS-generic "Paul Edwards" <mutazilah@gmail.com> - 2025-03-11 05:06 +1100
              Re: z/PDOS-generic scott@slp53.sl.home (Scott Lurndal) - 2025-03-10 19:01 +0000
                Re: z/PDOS-generic "Paul Edwards" <mutazilah@gmail.com> - 2025-03-11 08:04 +1100
                Re: z/PDOS-generic "Paul Edwards" <mutazilah@gmail.com> - 2025-03-11 08:47 +1100
            Re: z/PDOS-generic antispam@fricas.org (Waldek Hebisch) - 2025-03-11 18:15 +0000
              Re: z/PDOS-generic cross@spitfire.i.gajendra.net (Dan Cross) - 2025-03-11 18:29 +0000
                Re: z/PDOS-generic "Paul Edwards" <mutazilah@gmail.com> - 2025-03-12 05:52 +1100
                Re: z/PDOS-generic antispam@fricas.org (Waldek Hebisch) - 2025-03-11 23:05 +0000
                Re: z/PDOS-generic cross@spitfire.i.gajendra.net (Dan Cross) - 2025-03-11 23:48 +0000
                Re: z/PDOS-generic antispam@fricas.org (Waldek Hebisch) - 2025-03-12 02:23 +0000
                Re: z/PDOS-generic cross@spitfire.i.gajendra.net (Dan Cross) - 2025-03-12 02:34 +0000
                Re: z/PDOS-generic "Paul Edwards" <mutazilah@gmail.com> - 2025-03-12 18:41 +1100
      Re: z/PDOS-generic John Ames <commodorejohn@gmail.com> - 2024-07-19 09:35 -0700
        Re: z/PDOS-generic "Paul Edwards" <mutazilah@gmail.com> - 2024-08-21 04:20 +0800
          Re: z/PDOS-generic John Ames <commodorejohn@gmail.com> - 2024-08-21 09:51 -0700
            Re: z/PDOS-generic "Paul Edwards" <mutazilah@gmail.com> - 2024-08-22 13:24 +0800
      Re: z/PDOS-generic Grant Taylor <gtaylor@tnetconsulting.net> - 2024-07-19 19:46 -0500
        Re: z/PDOS-generic "Paul Edwards" <mutazilah@gmail.com> - 2024-08-21 04:18 +0800
    Re: z/PDOS-generic Salvador Mirzo <smirzo@example.com> - 2025-03-08 14:41 -0300
      Re: z/PDOS-generic cross@spitfire.i.gajendra.net (Dan Cross) - 2025-03-09 01:58 +0000
        Re: z/PDOS-generic Salvador Mirzo <smirzo@example.com> - 2025-03-10 09:31 -0300
          Re: z/PDOS-generic cross@spitfire.i.gajendra.net (Dan Cross) - 2025-03-10 14:28 +0000
          Re: z/PDOS-generic scott@slp53.sl.home (Scott Lurndal) - 2025-03-10 14:46 +0000

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