10 Jan
2013
10 Jan
'13
5 a.m.
On Wed, Jan 09, 2013 at 11:47:18PM -0500, David Riley wrote:
To bring it back, maybe: I'm
rather curious about DOS extenders. I know DOOM and
Quake both used 32-bit extenders to gain access beyond the
limitations of real mode, but I've never been quite clear
on what those extenders actually DID.
A 386 DOS extender puts the CPU into protected mode and loads a 32-bit
user program, while keeping DOS alive in a V86 box (286 DOS extenders would
have to switch in and out of genuine real mode) where it's blissfully unaware
that anything has changed. Then the DOS extender takes care of mode switching
so that the user program can make DOS calls, and handle hardware interrupts,
and map windows to memory-mapped hardware, and whatever else needs doing.
It's horrifying but also kind of beautiful -- all the benefits of an OS
that's too stupid to stop you from doing whatever you want, *and* tons of
memory.
John Wilson
D Bit