DOS ain't dead

PSP environment word as a selector - How is exec handled? (DOSX)

posted by ecm  , Düsseldorf, Germany, 25.01.2026, 19:15

> > I've heard that for some DOS extenders, the word [PSP:2Ch]
> may
> > be replaced by a selector that points to the environment, rather than a
> > segment address.
>
> It's not just what "some DOS extenders" do, but specified in DPMI:
> https://www.delorie.com/djgpp/doc/dpmi/ch4.1.html

Ah yes, indeed. However:

> If the client wishes to free the memory occupied by the environment, it should do so before entering protected mode and zero the word at PSP:2CH (segment address of the environment>.

I believe this (PSP environment field = 0) leads to a crash on MSW 98SE when running in a DOS window of the GUI, upon trying to enter Protected Mode.

---
l

Complete thread:

• PSP environment word as a selector - How is exec handled? - ecm, 22.01.2026, 12:24 (DOSX)
  • PSP environment word as a selector - How is exec handled? - tkchia, 22.01.2026, 16:54
  • PSP environment word as a selector - How is exec handled? - tkchia, 22.01.2026, 17:24
  • PSP environment word as a selector - How is exec handled? - Japheth, 25.01.2026, 18:02
    • PSP environment word as a selector - How is exec handled? - ecm, 25.01.2026, 19:15
      • PSP environment word as a selector - How is exec handled? - ecm, 25.01.2026, 19:21