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  The question of whether or not to use the DOS services arises naturally
  during the design and development of sophisticated programs. Our general
  advice, echoed throughout this book, is for you to use the highest
  available services that will accomplish what you need. This means that,
  whenever possible, you should use the built-in services of your
  programming language first, resorting only when necessary to direct use of
  the DOS services or the ROM BIOS services, and resorting only in extreme
  circumstances to direct programming of the computer's hardware.

  In practical terms, either a program can be written entirely within the
  confines of the programming language's facilities or nearly all of its I/O
  work must be done outside the programming language, at a lower level. When
  a lower level of programming is needed, with very few exceptions the DOS
  services are best suited for disk operations. When you are working with
  the keyboard or other I/O devices, either the DOS routines or the ROM BIOS
  routines will be adequate, depending on the application. But for low-level
  video-display programming, the situation is more complex. Satisfactory
  screen output almost always seems to call for the ROM BIOS services and
  direct hardware programming, even though in some cases screen output is
  best left in the hands of DOS. We'll see why in a moment.