It was thus said that the Great Richard Erlacher once stated:
>
> > MS DOS:
> > They bought a clone of CP/M
> >
> I used CP/M every day for about six years. When I saw my first MS-DOS, I
> noted that the console command for a file list was 'DIR' and 'TYPE' and
> that's where the similarity ended. The file system architecture and
> associated function set was totally different from CP/M's, and the console
> commands were different. What they had in common beyond 'DIR' was that they
> responded to keyboard commands just like ALL other OS'. CP/M used PIP
> rather than Copy. Are you now going to say they swiped that from OS-8? I
> just can't convince my self that there's much in common between MSDOS and
> CP/M.
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).
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.
You can also terminate a program by calling location 0000h (again, in a
COM program). In CP/M this causes a warm reset (similar functionality).
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.
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.
Microsoft's coming along and obtaining QDOS for $50,000 isn't that
straightforward but that's a story for another time.
> > MS Visual BASIC:
> > Now this one has bothered me for several years, did they buy the underlying
> > technology or copy something that already existed. I've a strange feeling
> > that this one was actual innovation!
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.
To my knowledge, the Apple ``Visual Basic'' never saw the light of day.
-spc (All on topic, stuff happened more than 10 years ago)
Received on Fri Apr 07 2000 - 14:13:47 BST
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