DOS code in CP/M? Revisited...

Fred Cisin cisin at
Wed Jul 13 23:25:56 CDT 2016

On Wed, 13 Jul 2016, Evan Koblentz wrote:
> Did MS-DOS use code copied from CP/M? Forensic software engineer Bob Zeidman 
> said "no" in 2012 but now he has new research to disclose at VCF West.
> That's all I can say for now. :)

THAT might be CP/M code in MS-DOS.

As to your subject line of "DOS code in CP/M", although a lot of the data 
structures, commands, and API are suspiciously similar ("we did that for 
software portability"), I doubt that any amount of studying of the code 
of CP/M will ever show that Gary Kildall copied anything from MS-DOS to 
write CP/M!   (although it is suspiciously similar to CMD.EXE in 

There was never any question about MS-DOS being a copy of CP/M in how it 
looked and worked.  THAT was never disputed.  It started as a work-similar 
PLACEHOLDER for SCP to use while waiting for DRI to release CP/M-86. 
BUT, in those days, work-alike was NOT considered to be infringing. 
(AND, Gary Kildall was not a very litigious person)

In those days, before "look and smell", it was generally considered 
perfectly acceptable to make an identical looking and behaving program, so 
long as none of the actual CODE was copied.  Perfectly acceptable to have 
all menus the same, and to make a RAC-MAN program.   ("Puckman" was one of 
the pre-release names of "Pacman" (character resembles a hockey puck), but 
somebody realized how easy it would be to change a 'P' into an 'F' on the 
face of the arcade machine.)

Adam Osborne when he started Paperback Software was going to get rich 
selling identical looking and behaving duplicates of popular software.
LOTUS changed the interpretations of copyright law.
If Adam were to have been just a touch quicker about going out and buying 
any of the debris failed companies from VisiCalc (several of which had IP 
rights to VisiCalc), then he could have filed a counter-suit against LOTUS 
and fought them off.
When Novell bought the remains of DRI, all that they really wanted was IP 
rights to CP/M, in case Microsoft ever sued them over copyright.
If Delrina were to have cut a deal with Jefferson Airplane to buy the 
rights to the album cover of Thirty Seconds Over Winterland, Berkeley 
Systems would have lost their case ("stealing the idea of toasters with 
wings")   (Am I the only one who considered the Opus and Bill 
screensaver to have been a Fair-Use parody?)

and, . . .
just like the DOS code in CP/M, . . . 
"The simplistic style is partly explained by the fact that its editors, 
having to meet a publishing deadline, copied the information off the back 
of a packet of breakfast cereal, hastily embroidering it with a few foot 
notes in order to avoid prosecution under the incomprehensibly torturous 
Galactic Copyright Laws. Its interesting to note that a later and wilier 
editor sent the book backwards in time, through a temporal warp, and then 
successfully sued the breakfast cereal company for infringement of the 
same laws."

More information about the cctalk mailing list