From: cross@spitfire.i.gajendra.net
In article ,
Waldek Hebisch wrote:
>Dan Cross wrote:
>> In article <87o6ybbeqw.fsf@example.com>,
>> Salvador Mirzo wrote:
>>>scott@slp53.sl.home (Scott Lurndal) writes:
>>>
>>>> "Paul Edwards" writes:
>>>>>Sure - but why not make it available anyway?
>>>>
>>>> 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)
>
>This is oversimplified definition, any definition of similar
>length will be oversimplified. But let us see how this
>works.
Mmm...not really.
>> 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.
>
>[snip]
>
>Also, you seem to ignore a file system. For definition
Funny how in the very next paragraph you quoted, I was talking
about a filesystem. ;-P
>above to make any sense multipling machine hardware
>resources must include mutiplexing (coordinating) access
>to external storage which is (part of) function of file system.
>
>> While it does provide a primitive filesystem,
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
(See note above)
>> 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. Further,
>> the system interface is inexorably tied to the hardware; it's
>> defined in terms of synchronous software traps and specific
>> register values. System calls are numbered, not named.
>
>System calls are numbered in almost all operating systems.
You're talking about the ABI.
>[snip]
>> Finally, the last one is really the nail in the coffin: MS-DOS
>> makes absolutely no effort to protect the software principles
>> from each other, or even themselves; a user program can take
>> over and just never cede control back to DOS.
>
>Well, DOS is close to best possible protection given the
>hardware. In modern times hardware protection gained
>importance, but putting hardware protection as mandatory
>part of operating system definition distorts history
>quite a lot.
By the time the IBM PC came along, we'd had systems where the
OS was protected from errant programs for 20 years. For example
look up the Manchester Atlas system.
>There is a lot of valid critique of DOS, but saying that it is
>not an OS is just silly game of words. You can pile adjectives
>on OS, like "multitasking OS", "proteded OS" (or better
>"OS using hardware protection") and DOS will be outside such
>restricted classes of OS-es. But is clearly an OS.
Well, except perhaps it is not. At least not by a very
reasonable definition that's widely accepted in the field.
I really don't see why people are so upset about this; it's not
a huge deal. DOS was ok for it's time and for what it enabled
on the original IBM PC; the hardware was very limited, and so it
wasn't nearly as capable as larger systems with "real" operating
systems. Why is it a priori a bad thing to acknowledge that?
It sure seems like some people are getting worked up about a
very minor thing.
- Dan C.
--- SoupGate-Win32 v1.05
* Origin: you cannot sedate... all the things you hate (1:229/2)
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