This is the _Atari_System_Reference_Manual_ (c) 1987 by Bob Duhamel.
It's a very huge text file with 20 chapters:
  Central Input Output Utility (CIO)
  Disk Operating System (D:)
  Using the DOS 2 Utilities (DUP.SYS)
  Cassette Handler (C:)
  Keyboard Handler (K:)
  Printer Handler (P:)
  Screen Editor (E:)
  Display Handler (S:)
  Resident DIsk Handler
  System Interrupts
  Floating Point Arithmetic Package
  Boot Software Formats
  Serial Input/Ouput Interface (SIO)
  Hardware Chips
  Display Lists
  Player And Missile (PM) Graphics
  Sound
  Joystick Ports
  Misc
  XL and XE Models

I hope you enjoy it!  - bill     Kendrick@VAX.Sonoma.Edu