3 ms·

I suspect it’s 80% straightforward and 20% bug compatibility

• stevekemp 11mo ago
  Very much so. If programs are well-behaved, and call "int 21", etc all is well. But a lot of programs would use undocumented things, such as the list-of-lists and they'd directly peek and poke into the operating systems code. I've had fun updating the shell, and code, of CP/M, in assembly, and writing emulators of it. But as always there is no shortage of programs making specific assumptions that make everything more complex than they should be.
  • ssrc 11mo ago
    I remember the books on undocumented functionality like https://archive.org/details/Undocumented_DOS https://archive.org/details/Undocumented_DOS
    • cout 11mo ago
      I remember that book! I wanted to get a copy but made do with the DOS Programmer's Reference, 3rd ed., which was also very good since beej's interrupt list wasn't available yet or I didn't know about it.
      • rzzzt 11mo ago
        Was it Ralf Brown? beej has C and networking tutorials: https://beej.us/guide/ https://beej.us/guide/
        • cout 11mo ago
          Yes, Ralf Brown. I guess I'm getting old.
          • rzzzt 11mo ago
            I found a copy of the PC Game Programmer's Encyclopedia (PCGPE) back then but couldn't really wrap my head around most of the articles (especially the 3D stuff and Mode X).