This documentation describes the Bally Home Videogame System, otherwise known as the Bally Professional Arcade, Bally Home Computer, or Bally Astrocade.

System routines are divided into five categories based upon their functions:

• The User Program Interface allows cartridges to reference the system routines through a standard interface, including an interpreter.

• The Screen Handler provides routines for creating screen images, including facilities for initialization, pattern, and character display, coordinate conversion, and object vectoring.

• The Human Interface reads keypad / control handle inputs and handles game selection and options.

• The Interrupt Scheduler handles systems dependent upon timing, i.e., counters, timers, music, and interrupts.

• The Math routines manipulate BCD and decimal numbers and store/transfer data.

NOTE: The Nutting Manual lists slightly different system subsections on its opening page, within the system routine descriptions, and in the operating system source listing. The Better Bally Book favors the subsections organized in the source listing (pp. 6–7) both due to their logical organization and due to their complete listing of otherwise undocumented system routines.