DOS ain't dead

OS/2 extender (Developers)

posted by kerravon , Ligao, Free World North, 12.09.2025, 00:08

> > I was considering disabling interrupts, entering 64-bit mode, doing all
> my
> > work above 4 GiB, and then when I need any service, switching back to
> > 32-bit mode and reenabling interrupts.
> >
> > Presumably exactly the same as DOS extenders did, especially DOS
> extenders
> > written prior to DPMI existing (I think that's a thing).
> >
> > You think the above scheme won't work?
>
> No. That's the protection in "protected mode" at work.
>
> It works in DOS, as there is no protected mode operating system running
> that prevents programs from switching processor modes like crazy.

I don't understand.

First of all - both PM32 and LM64 are "protected mode", I believe.

Secondly, so long as I have privilege, there is nothing preventing me from switching from PM32 to LM64.

You could argue that when I return to PM32, everything will blow up because I've messed everything up.

But I believe everything can be restored to how it was before.

So long as I only touch memory above 4 GiB, OS/2 won't even be aware that anything has happened. The most it could possibly detect - if it tried hard - was that interrupts were disabled for "quite a while".

Complete thread:

• OS/2 extender - kerravon, 10.09.2025, 21:05 (Developers)
  • OS/2 extender - Rugxulo, 10.09.2025, 21:30
  • OS/2 extender - Ringding, 11.09.2025, 17:44
    • OS/2 extender - kerravon, 11.09.2025, 17:57
      • OS/2 extender - Ringding, 11.09.2025, 20:41
        • OS/2 extender - kerravon, 12.09.2025, 00:08
          • OS/2 extender - Rugxulo, 12.09.2025, 04:07
            • OS/2 extender - kerravon, 12.09.2025, 16:55
          • OS/2 extender - Ringding, 12.09.2025, 17:20
            • OS/2 extender - kerravon, 12.09.2025, 18:03