DOS ain't dead

From 0 to 1 MB in DOS / Beyond the 1 MB barrier in DOS (Developers)

posted by kerravon, Ligao, Free World North, 14.02.2024, 11:51

> Another two articles by Julio Merino:
>
> From 0 to 1
> MB in DOS
> A tour on how DOS was able to use most of the 1 MB address space of the
> 8086
>
> Beyond
> the 1 MB barrier in DOS
> Continuing the tour on how DOS apps used memory above the first MB

Thanks for that - it was interesting - especially seeing
what expanded (not extended) memory was, and an actual card.

One thing that wasn't covered though - they said there were
gaps in the memory above 640k that could be used. But no
mention of banking out even used memory, which I believe
was possible.

Although you would need a replacement for MSDOS to do
that I guess (still 8086 though).

So if you have a CGA at 0xb8000 - before you do the
BIOS call that writes to the screen, bank the CGA
back in.

That also required cooperation from the applications
though - to not manipulate the hardware directly.

So not very useful for existing programs, but something
I could potentially add to PDOS/86 to support applications
that "follow the rules".

I've only done very brief investigation - just to ask
the question of whether banking was possible, and got
an answer of "not impossible".

It would be good to have a cooperative BIOS that
minimized its footprint too, so that it could be
banked out itself.

Although to some extent it's all fairly pointless.
If you have a properly-written program it can run
on an 80286 using the Family API anyway. Or
something similar. Or what I was planning on doing -
OS/2 1.x for the 8086 to run the Family Mode
applications without the actual Family Mode code in
the executable.

BFN. Paul.

Complete thread:

• From 0 to 1 MB in DOS / Beyond the 1 MB barrier in DOS - rr, 13.02.2024, 21:51 (Developers)
  • From 0 to 1 MB in DOS / Beyond the 1 MB barrier in DOS - kerravon, 14.02.2024, 11:51
    • From 0 to 1 MB in DOS / Beyond the 1 MB barrier in DOS - marcov, 14.02.2024, 11:59
      • From 0 to 1 MB in DOS / Beyond the 1 MB barrier in DOS - kerravon, 14.02.2024, 12:53