Ibm s-100 system?

Fred Cisin cisin at
Sat Apr 23 19:09:36 CDT 2016

On Sat, 23 Apr 2016, william degnan wrote:
> I have a copy of a MS or IBM DOS for my CompuPro on 8" disk, I think it's
> v. 1.25.

1.25 would be MS-DOS.  The PC-DOS equivalent was 1.10
("equivalent", NOT exactly the same (GWBASIC, MODE.COM differences, 

MS-DOS 1.25 could be configured by OEM for various disk formats.
At that time, MS-DOS was not available for direct retail sale.  "Only 
available from computer OEM".  OEMs could sell it retail to buyers of 
their computers, and theoretically ONLY to them.  In reality, few OEMs 
wanted to, nor bothered to, confirm "legitimacy" of their customers, 
and many OEM copies found their way to retail sales. ("gray market")  In 
fact NO version of MS-DOS was legally retail until 5.00.  MANY OEMs let 
out "OEM" MS-DOS for retail sale by third parties.
PC-DOS 1.10 was 160K and 320K ONLY.
Many OEM versions of MS-DOS 1.25 (such as Compaq) deliberately lockstepped 
with IBM, and did not offer any diverging capabilities.   For many of 
those OEMs, the main thing that they had to offer was a [cheaper] way to 
get a 5150, with possibly some clever developments.

> I also have a copy of 1.25 on my CBM 256x, with 8086
> co-processor.   Neither of these were BEFORE the original IBM PC, but hint
> at a time when there was a "DOS" in development floating around before the
> actual IBM system.  This DOS could have been demoed in Europe on an S-100.
> lots of conjecture here.  Just speculating.
1.25 could NOT have been demoed in Europe, nor anywhere else until 1982, 
well after the 5150.

HOWEVER, it is entirely possible that that "IBM S-100" was merely a 
Seattle Computer Products S100, or even an SCP 8086 CPU board in a 
Cromemco S100 system, with a piece of tape changing the name.
(In order to "test the waters' about how an IBM 808x machine would be 

1.00 came out in August 1981.
PC-DOS 1.10 came out in May 1982.
MS-DOS 1.25 came out in June 1982.

The existence of later versions AFTER the first one, does NOT "hint at a 
time when there was a DOS in development floating around before" the first 
one. Existence of a later version never hints at presence of something 
before the first one, although CONTENT might give some clues of what was 
being considered at various times.  It hints at further development, and 
the possibilities of spreading out into areas where IBM did not tread.

But, YES, the very first version WAS for an S100 machine made by Seattle 
Computer Products.  Written by Tim Paterson, it was called "QDOS" (Quick 
and Dirty OS), and then "86-DOS".  (and, for a while, "SB-86")  YES, it 
supported 8".

Then, in July 1981, SCP sold it to Microsoft, who handed off to IBM.

Microsoft's contract permitted them to sell it to other computer OEMs, but 
ONLY through other computer OEMs.  THAT restriction ended in 1991, 
commemorated with MS-DOS 5.00.

After Microsoft upgraded PC-DOS from 1.00 to 1.10, they then provided 
computer OEMs with a similar product numbered 1.25
OEMs were expected to make their own personalized and customized IO.SYS, 
MODE.COM (could also do stuff such as switching between internal/external 
monitor, etc.), etc.
OEMs did not even need to call it "MS-DOS"  (Zenith Z-DOS)

Trivia: there was no one point one.  it was one point ten.
Internally, the minor version of the OS was stored as a two digit decimal 
number, obviously stored in binary.  Thus, "1.1" was stored as a 1 and 
MOV AH, 30h
INT 21h
returns major version in AL, minor in AH.  "1.1" returns 0A01, 1.25 
returns 1901, 3.30 returns 1E03, etc.

Grumpy Ol' Fred     		cisin at

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