segmented memory models

[Chuck Guzis]

On 3 Aug 2008 at 23:28, Sridhar Ayengar wrote:

> I do design for a living, and, although your point regarding being 
> unable to predict the future with perfect accuracy rings true, I would 
> argue that prototypes really help with getting the really big screw-ups 
> out of your designs.

I consider neither the reset vector nor the segmentation feature of 
the 80x86 to be a design screw-up, but rather a design decision.  
Regardless of the technical quibbling, it works.

Real screw-ups are the "you can't get there from here" sort--where 
there are no good work-arounds and the problem prevents customers 
from getting useful work done.   Sometimes, this stems from a 
misunderstanding of the customer's needs.

For example, on the 80286, I can imagine an engineer saying to 
himself "Once you've entered protected mode, why would you *want* to 
go back to real mode?" Hence, the really weird kludge using the 
keyboard controller to reset the CPU into real mode on the PC AT.

Without the then-undocumented LOADALL instruction, protected-mode 
Windows may have been delayed until the 80386.  Quel horreur! 

Cheers,
Chuck