Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!csd4.milw.wisc.edu!dogie.macc.wisc.edu!uwvax!umn-d-ub!umn-cs!ns!ddb
From: ddb@ns.network.com (David Dyer-Bennet)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Why unix doesn't catch on
Keywords: multitasking
Message-ID: <1308@ns.network.com>
Date: 20 Apr 89 20:29:19 GMT
References: <1922@dataio.Data-IO.COM> <101000047@hpcvlx.HP.COM> <199@isctsse.UUCP> <1292@ns.network.com> <2899@rti.UUCP>
Reply-To: ddb@ns.UUCP (David Dyer-Bennet)
Distribution: usa
Organization: Terrabit Software
Lines: 50

In article <2899@rti.UUCP> bcw@rti.UUCP (Bruce Wright) writes:
:In article <1292@ns.network.com>, ddb@ns.network.com (David Dyer-Bennet) writes:
:> In article <2890@rti.UUCP> bcw@rti.UUCP (Bruce Wright) writes:
:> :
:> :The old multitasking operating systems for things like the PDP-8
:> :and so forth required application programs which cooperated with the
:> :operating system.
:> 
:> Ummm, this turns out not to be the case.  TSS-8 on a PDP-8I had hardware
:> protection against the timeshared tasks doing anything that would damage
:> the rest of the system.
:
:Although I was (partly) thinking about operating systems which had no
:hardware protection, I really was addressing a completely different
:problem:  None of these small-machine operating systems (with or without 
:hardware protection) provided ANY kind of emulation for programs which
:insisted on making direct hardware I/O calls.  All of them that I am
:aware of would simply terminate the offending program (if they could
:and if they got an appropriate interrupt to find out about it).

Still not completely true.  The "test for character available" and "read
character" (from tty) hardware instructions were trapped and emulated by
TSS-8, as were most of the other character-at-a-time device instructions.
In fact TSS-8 was smart enough to recognize the busy wait loop and stop
running it (providing its own non-busy wait).  There were TSS-8 native
sys calls that avoided this, but these emulations were provided for
compatibility with previous standalone programs.

Now, I think this is pretty much a side-issue, and doesn't affect the
validitiy of your basic argument, so I'll shut up now.  But TSS-8 was
the first timesharing system I ever saw, and I'm STILL impressed with
some of the things it managed to do on a system with 32k memory if
fully configured.  

:The unfortunate situation that the PC world has backed itself into is
:one that requires that any environment that provides "PC emulation" must
:also emulate the HARDWARE environment (with all its quirks ....) of a
:real PC.  It's not enough to just provide DOS or even BIOS compatibility.
:From a software design point of view, this is an almost unspeakable
:abomination, one that we will regret for many years.

Yes, exactly, I agree, precisely, good point, definitely.  Of course, they
*did* get some pretty zippy Lotus performance on floppy-based systems on
the plus side; but like most contracts with the devil, it's probably not
worth it in the long run.
-- 
David Dyer-Bennet, ddb@terrabit.fidonet.org, or ddb@ns.network.com
or ddb@Lynx.MN.Org, ...{amdahl,hpda}!bungia!viper!ddb
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