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  DOS uses three interrupts, 22H through 24H (decimal 34 through 36), to
  handle three exceptional circumstances: the end of a program, a "break"
  keyboard action (Ctrl-Break or Ctrl-C on the standard PC keyboard), and
  any "critical error" (usually a disk error of some kind). Your programs
  can affect the action taken in each of these three circumstances by
  changing the corresponding interrupt vector to point to any operation you
  choose. This is why we call these interrupts the address interrupts.

  DOS maintains a default address setting for each of these interrupts,
  which is preserved at the beginning of a program's operation and restored
  after the program is finished. This allows your programs to freely change
  these vectors according to their needs without disturbing the operation of
  subsequent programs or the operation of DOS itself.