Re: It's all software (I _think_)

Subject: Re: It's all software (I _think_)
From: "Arlen P. Walker" <Arlen -dot- P -dot- Walker -at- CORE -dot- CORP -dot- JCI -dot- COM>
Date: Thu, 18 Aug 1994 09:54:01 -0500

I promised myself I'd just post the once on this topic. I'm breaking that
promise. My apologies for the techie-talk, but I felt I had to point
something out. Last time, I promise. (And *this* time I mean it. :{>} )

>A Macintosh -- Motorola or PowerPC-based -- will not run OS/2 today. For
>a Mac to _run_ OS/2, System 7 could not be running.

This statement makes no sense. Let me elaborate:

When a machine (*any* machine, not just a mac) runs a software emulation of
a particular chip, the details of the OS the emulation is running under do
not enter into the equation. For example, it is perfectly possible (and I
have done this) to run the emulation of a propreitary chip (in this case
the LSI-11) on a completely different processor with no ill effects. What
happens is the software reads the instruction, looks up what that
instruction does, and then does it. If it reads an ADD instruction, it
loads the values from their respective locations and adds them. How it gets
them is irrelevant to the software running under emulation, as the
emulation makes it appear as if it got them from exactly the place and in
exactly the manner that the emulated software requested them. Every
function of the CPU is mimicked precisely within the emulation. Any
software which runs within this emulation has no direct contact with, and
no knowledge of, the OS the emulation is running under. Any software which
can run on the chip being emulated will run within the emulation.

I think perhaps what you were getting at was that system 7 is not
pre-emptive, while OS/2 is, and you think you can't one run model within
the other. This isn't exactly true (you can even do pre-emptive
multi-tasking within DOS, after a fashion -- in my younger days I wrote a
data collection and analysis system which did just that). OS/2 can do
pre-emptive multi-tasking within the emulator, it's just that the emulator
is doing co-operative multi-tasking with the rest of the world. In other
words, what OS/2 sees as clock cycles, are not real clock cycles but
emulated ones, so OS/2 can base anything it wants with the clock cycles it
sees without interfering with the OS the emulation is running under.

I should note that I haven't examined the Houdini card series in any
detail, so I can't address the finer details of them. I *have* however seen
and worked with SW-based chip emulations running on several platforms (we
have some in-house for embedded systems development in the engineering
labs, and I'm a curoius guy) ranging from Windows and Mac to VMS.

And on a related topic: within an application, the Mac supports two types
of threading, co-operative *and* pre-emptive.

>If a Mac did run OS/2, it would be one hell of an improvement. Apple
>is on the right track with their future plans for System 7 on the

I'll give a perhaps to that first statement (once OS/2 2.1 arrived, I
thought it looked interesting -- just not interesting enough to walk away
from what I already had) and an "Amen" to the second. I'm going to really
enjoy the next few years in the wonderful world of micros.

Have Fun,

arlen -dot- walker -at- jci -dot- com
IN GOD WE TRUST --- All others must provide data

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