FreeVMS

From: Eric J. Korpela <korpela_at_ssl.berkeley.edu>
Date: Sat Jan 5 00:40:00 2002

> On Fri, 4 Jan 2002, Sean 'Captain Napalm' Conner wrote:
> I believe that in virtual-8086 mode, priveleged instructions (e.g. OUT)
> cause a trap. The OS, having set up the appropriate trap gates, gets
> control and decides what to do for these instructions.

There is a bit mask in the TSS (I think) that controls whether an I/O
will trap or be executed. Other privledged instructions will trap.

> > There is an undocumented mode---real-32 bit (where the CPU is in
> > 32-bit mode, but not running protected) but that's a hack and is
> > probably not recomended.
>
> That's 'flat mode'.

I think he means "real flat mode" which is different from what
is usually referred to as "flat mode."

Eric
Received on Sat Jan 05 2002 - 00:40:00 GMT