DOS ain't dead

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

posted by ecm  , Düsseldorf, Germany, 22.01.2026, 12:24

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.

If this is so, does the extender swap around the PSP field around exec calls? If DOS is given a zero in the exec block for the environment source, it'll retrieve the environment from the current PSP. But DOS expects a segment in that field.

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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