DOS ain't dead

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

posted by tkchia , 22.01.2026, 17:24

Hello ecm,

Another interesting tidbit: if CauseWay is running in "DOS/4G" mode -- which happens if the client program does a DOS/4G installation check -- then the environment address field in the parameter block is actually a 48-bit selector:offset address, not just a selector value. Shenanigans.

Thank you!

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https://codeberg.org/tkchia · https://disroot.org/tkchia · 😴 "MOV AX,0D500H+CMOS_REG_D+NMI"

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