Re: 80286 protected mode

John Levine <johnl@taugh.com> writes:

According to Anton Ertl <anton@mips.complang.tuwien.ac.at>:

Here's another speculation: The 286 protected mode was what they
already had in mind when they built the 8086, but there were not
enough transistors to do it in the 8086, so they did real mode, and in
the 80286 they finally got around to it.  And the idea was (like AFAIK
in the iAPX432) to have one segment per object and per procedure,
i.e., the large memory model.

>
If you look at the 8086 manuals, that's clearly what they had in mind.
>
What I don't get is that the 286's segment stuff was so slow.

It had to load the whole segment descriptor from RAM and possibly
perform some additional setup.

- anton
--
'Anyone trying for "industrial quality" ISA should avoid undefined behavior.'
  Mitch Alsup, <c17fcd89-f024-40e7-a594-88a85ac10d20o@googlegroups.com>