Int 20h                 Terminate Program
 Int 21h                 DOS System Function
 Int 22h                 Termination Address
 Int 23h                 Ctrl-C Handler
 Int 24h                 Critical-Error Handler
 Int 25h                 Absolute Disk Read
 Int 26h                 Absolute Disk Write
 Int 27h                 Terminate and Stay Resident
 Int 28h                 DOS Idle Handler