It was thus said that the Great Richard Erlacher once stated:
>
> > The similarities of MS-DOS to CP/M are mostly internal. In looking over
> > the list of OS functions between the two, the first 36 functions of each are
> > the same, with a few notable exceptions where the concept don't match
> > (MS-DOS for example does not have an IOBYTE).
>
> What of those things internal would you have had them leave out in order to
> be more different from CP/M, which was a VERY popular OS at the time,
> without removing its functionality. Since the features to which you refer
> are internal, I assume you have precice citations of common source code,
> right? They're certainly not obvious to me in my role as a fairly frequent
> user.
Well, the question on the table was the similarities between CP/M and
MS-DOS which you didn't see outright because you only noticed the external
side of each (user commands). All I did was show that the similarites were
a bit deeper than just the user commands.
And to make the comparrison all I had to do was lookup the operating
system functions between the two. For example, the first twelve functions:
# CP/M MS-DOS
---------------------------------------------------------------
1 Read console Character input with echo
2 Write console Character output
3 Read reader Auxilliary input
4 Write punch Auxilliary output
5 Write list Printer output
6 Direct console I/O Direct console I/O
7 Determine IOBYTE Unfiltered character input w/o echo
8 Set IOBYTE Character input w/o echo
9 Print buffer Display string
10 Read buffer Buffered keyboard input
11 Return console status Check input status
12 Return version Flush input buffer then input
It's hard to say how I would design an OS for CP/M class (or early MS-DOS
class) machines; hind sight and all that. And I'm not even saying it was
wrong for Tim Patterson to model the OS calls after CP/M. After all, that's
what he knew.
Although I might be more inclinded to remove redundant calls (that differ
only in device) but that's a step down the Unix direction.
> > There are also two ways to call MS-DOS functions, one through the
> > documented interrupt call (INT 21h), the other a call to location 0005h
> > (that is, for a COM program consisting of a single segment, calling location
> > 0005h in the current segment has the same effect of calling INT 21h---for an
> > EXE program you may not be able to do it since the PSP (the segment the call
> > lives in) is in a different segment than the rest of the program
> > typically)), which is how you call BDOS in CP/M.
> >
> Since there is only one segment in CP/M, I guess you've got 'em there. Of
> course it really doesn't matter what the location is, does it? I guess any
> OS that load a register and then calls a specific location is a copy of
> CP/M, right?
Not outright. And it's not like MS-DOS used that as the ONLY way to call
the operating system---the preferred method was still INT 21h. I suspect it
was only put in to help migrate software from CP/M to MS-DOS.
> >
> > The register usage is different, but that's only to be expected because of
> > differences between the 8080 and 8086, but 8080 code could be mechanically
> > translated to 8086 since there was a one-to-one relationship between
> > registers. It wouldn't produce optimal code, but it would produce code that
> > would more or less work and these register mappings map pretty well between
> > the CP/M and MS-DOS calls.
>
> The mapping of one register set into the other is not an accident. Ask
> Intel about that!
Why bother, I know the register mapping was intentional to help the
migration of source code (mostly in assembly) from the 8080 to 8086. It was
Motorola that took a large gamble at the time in making the 68000
incompatible with the 6800 line in all respects.
> I'm told that CP/M-86 is considerably more than a
> translation of CP/M-80. Now you suggest that the roots of MS-DOS are
> entirely in CP/M? They may have common roots, as they reflect the then
> conventional wisdom about how one should write a microcomputer operating
> system. It should be no surprise to anyone that there are some
> similarities. One doesn't want to ignore what works just because it wasn't
> invented in house.
I would say that the roots of MS-DOS 1.x are entirely in CP/M, while with
2.x the influence of other operating systems (notably Unix) start to show
up. Then again, CP/M wasn't created wholecloth either, it had roots from
RT-11 (I think that's the OS), which Gary Kildall had experience with.
> After all, Pascal is not a copy of Algol just because it
> uses mnemonic variable names.
I'm not sure what you mean by that. Yes, Pascal and Algol are in the same
family of computer languages but a Pascal source code does not an Algol
program make.
> > Tim Patterson, who wrote the initial version of MS-DOS while at Seattle
> > Products, may have had access to CP/M sources since Seattle Products sold
> > CP/M systems and they were working on an 8086 based computer in the late
> > 70s. Tim probably modeled his QDOS (Quick-n-Dirty Operating System) closely
> > after CP/M (some say he may have mechanically translated CP/M since
> > copyright statements to Digital Research have allegedly been found in MS-DOS
> > 1.x but I haven't seen any). Why not? It would have been a quick and easy
> > way to get an OS for the 8086 system up and running.
>
> I've heard that, too. Does that mean that anyone who writes a program to do
> what he's seen another program do is making a copy?
Ask the lawyers or philosophers.
> You're not even sure he
> actually saw and read the source code. How many programmers do you know
> who'd simply copy someone else's work in a case like this? Everybody wants
> to leave his own mark.
I don't know about then, but now I would suspect that most programmers
would simply copy without bothering to leave their own mark (in case you
might not have picked up on it, I don't hold programmers in very high
reguard and I'm a programmer! Most programmers can't these days, as I'm
sure Tony would say most electrical engineers today can't either).
> > Microsoft's coming along and obtaining QDOS for $50,000 isn't that
> > straightforward but that's a story for another time.
> >
> Buying something that shortens your burden is kind-of like buying an
> integrated circuit rather than making the thing yourself starting with a
> wheelbarrow of sand. The fact that Microsoft knew that IBM had gone to
> Kildall probably told them what they wanted was sort-f like CP/M.
Like I said, the story of MS-DOS isn't that straightforward. Bill Gates
even told IBM to check with Digital Research for their OS. It was only when
IBM came back saying they were having negotiation difficulties with DR did
Bill Gates offer them an OS from Microsoft.
Bill Gates knew of QDOS and worked with SCP to licence it from them,
without telling SCP who their primary customer was. SCP was a bit peeved
when it learned that Microsoft's customer was IBM.
It wasn't until a few years later did Microsoft buy QDOS outright, after
SCP had gone bankrupt.
> > Apple was working on a version of BASIC for the Macintosh that would
> > resemble VB today in the late 80s/early 90s. Microsoft got wind of it and
> > threatened to cut their license to Microsoft BASIC for the APPLE II (still
> > amoney maker at the time) if Apple actually released the product. Apple
> > towed the line and what do you know---Microsoft produces this very
> > innovative product called Visual Basic shortly thereafter, but for Windows.
> >
> ... and now you'd like me to believe that MS knew this and copied it?
> Frankly, if I'd been in Billy's place, knowing that Apple had considered it
> would have scared me off.
This is Bill we're talking about here ... 8-)
-spc (Amature computer historian ... )
Received on Fri Apr 07 2000 - 20:12:28 BST
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