Date: Wed, 17 Mar 93 08:21:05 EST
From: DJ Delorie <dj AT ctron DOT com>
To: S0R1282%tamzeus DOT bitnet AT nic DOT near DOT net
Cc: djgpp AT sun DOT soe DOT clarkson DOT edu
Subject: Re: DPMI and VCPI


>All this talk about DPMI and VCPI has got me curious.  Can someone point
>me to a reference describing the two, and relative merits of each?  E-mail
> would be best to avoid excess traffic, and if there is interest I will
>post information.  Or am I the only one who does not know much in the way
>of details about these? thanks,

TopDown allocation - nobody is using anything, do whatever you want
with the system.

XMS - you must ask politely for extended memory and A20 control
services, otherwise you can do what you want.

VCPI - allows you to get into protected mode when you're in V86 mode.
Assumes you will take over the CPU, but you have to ask VCPI for
memory.  You run with no protection.

DPMI 0.9 - allows you to run a protected mode app.  Does not let you
take over the CPU, and protection is enabled (other programs might be
running).  Hooks for some protected services (debug registers, memory
allocation, interrupts).

DPMI 1.0 - adds linear mapping and true virtual memory.