title: What is INT 21h?
body: <p>Inspired by this question</p>
  
  <p><a href="https://stackoverflow.com/questions/1237489/how-can-i-force-gdb-to-disassemble">How can I force GDB to disassemble?</a></p>
  
  <p>I wondered about the INT 21h as a concept. Now, I have some very rusty knowledge of the internals, but not so many details. I remember that in C64 you had regular Interrupts and Non Maskable Interrupts, but my knowledge stops here. Could you please give me some clue ? Is it a DOS related strategy ?</p>