Click above to get retro games delivered to your door ever month!

  When you inspect the full range of tools and services placed in your hands
  by programming languages, by DOS, by the ROM BIOS, and by the computer's
  hardware, it becomes quite clear that the richest concentration of
  disk-oriented services exists at the DOS level. This almost goes without
  saying, because DOS, as a disk operating system, is inherently strongest
  in its support of disk operations.

  As discussed in Chapters 16 and 17, the majority of services that DOS
  performs are directly connected to the manipulation of disk files. Even
  some services that are nominally controlled by a program, such as loading
  and executing another program (interrupt 21H, function 4BH), involve
  disk-file operations. From this perspective, DOS is not so much a disk
  operating system as it is a system of disk services designed for use by
  your programs. When you are developing programs for the IBM personal
  computer family, you should approach DOS from this standpoint: Think of
  DOS as a cornucopia of disk operations placed at your service.