80286 Protected Mode Test

Fred Cisin cisin at xenosoft.com
Sun Mar 14 15:42:20 CDT 2021

On Sun, 14 Mar 2021, Guy Sotomayor via cctalk wrote:
> There were many heated discussions in various task forces (this was of course 
> IBM) about the next generation OS (to become OS/2) about the '286.  First 
> and foremost was how to be able to run DOS programs on the '286. Over very 
> vocal opposition, management decided to use "mode switching" rather than any 
> of the other techniques.  It should be noted, that a significant portion of 
> us advocated abandoning the '286 in favor of the '386 to solve this 
> problem.  The argument that management made against that approach assumed 
> that OS/2 would be ready in 9 months and that the '386 would be late ('386 at 
> the time was about 12-18 months away).  It turned out that OS/2 took well 
> over 18 months to develop.

The 80286 was an important step.  Getting 24 bits of address, instead of 
20 was significant.  It is too bad that they weren't able to set it aside 
until they got the next couple of steps (ala 80386) to be able to make 
better use of those address bits.

HIMEM.SYS (enabling A20 and using it to "overflow" past 1MB by 65K-16) 
became a ubiquitus kludge.

Gordon Letwin (the Microsoft author of OS/2) said that mode switching on 
80286 was "like turning off the car to change gears."
Even Bill Gates said that the 80286 was "BRAIN DEAD".

Segment:Offset had been developed as a kludge to be able to expand from 16 
bit address (64K), while maintaining almost full compatability.

Yes, a flat memory model IS the way to go.  But, they couldn't see a way 
to abandon Segment:Offset without abandoning compatability with all 
previously existing software.  Programs, such as Wordstar were ported from 
CP/M to PC in significantly less time than it took to re-edit their 

In contrast, Apple chose to abandon compatability with all previously 
existing software, and did have a period of time with nothing but 
Mac-Write, Mac-Paint, Wac-Write, and Mac-Paint.

Grumpy Ol' Fred     		cisin at xenosoft.com

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