Address - The unique location in memory of a program instruction, data or I/O register.
Analog - A signal that varies continuously, as opposed to a digital signal.
AND - A logical function that returns true only if both inputs are true, otherwise it returns false.


Bank-Switch - A method used to enlarge a CPU's memory space by using control signals to select one group of memory ICs from several that occupy the same addresses in memory.
Blitter - See Special Chip.


Chip - see IC.
CMOS - a type of low-power IC.
Code - see Software
Control Panel - The joysticks, buttons, etc. used to play a game.
CPU - Central Processing Unit - The IC that is the brains of the game. Classic Williams games use the Motorola 6809 for the game play, and the 6808 for the sound board.
CPU Board - The game board that contains the CPU and RAM. <description>


Digital - Data consisting of discrete states: on/off, 1/0 or high/low.
Digital To Analog Converter - An IC that provides a digital output from an analog input.
Digitize - To convert a signal from analog to digital form. Generally used to input sounds to a game.


Easter Egg - A hidden screen in a game, usually difficult to find. Included ostensibly for copyright/piracy reasons. <description>
Emulator - A program that mimics a piece of hardware. Video game emulators use the ROM images from actual games, instead of having a programmer rewrite the game from scratch. This results in much more authentic game play. Emulators are complex because they have to be able to perform the functions of several pieces of hardware, including graphics and sound subsystems and the CPU.



see logic gate


Hack - to mess around with software or hardware on a very low level, or a modification to someone else's software or hardware.
Hardware - The electrical, electronic and mechanical parts of a system, as opposed to the software.


IC - Integrated Circuit - One of many electronic devices (chips) that range from simple logical gates to complex CPUs.
Interface Board - See PIA board.
I/O - Input / Output.




logic gate - a simple electronic circuit, providing the function AND, OR, NOT, NOR, NAND, etc. There are usually several located on one IC.



NAND - A logical function that returns false only when both inputs are true, otherwise it returns true.
NOR - A logical function that returns true only when both inputs are false, otherwise it returns false.
NOT - A logical function that returns true when its input is false, and false when its input is true.


OR - A logical function that returns false only when both inputs are false, otherwise it returns true.


Patchfile - A text file that contains information on how to modify one file into another, usually by listing offsets into the file, and what to change that byte's value to.
PCB - Printed Circuit Board.
PIA - Programmable Interface Adapter. An IC (designated 6821) that allows the CPU to interact with other devices. On the Williams games, several of these are used to talk to the sound board, read the control panel, etc.
PIA Board - The game board that contains the control panel PIA. Also known as the Widget Board or Interface Board. <description>
Power Supply - A system that provides regulated voltages.
Power Supply Board - The game board that converts the low voltage A/C power to regulated DC power. <description>



RAM - Random Access Memory. ICs that contain temporary data used by a program. There are two types of RAM: Dynamic RAM contents are lost when the power is turned off, while Static RAM can be battery-backed up. The Williams CPU board contains 24 DRAM chips for screen buffer and program use.
Register - A location in a CPU that contains status or input data, or allows output of data.
ROM - Read only memory. ICs that contain permanent data or program code. ROM contents are preserved when the power is turned off.
ROM Board - The game board that contains the program ROMs. Most of the Williams games use 12 ROMs to hold the programs and data. <description>
ROM Images - Files containing the data stored on one or more ROM chips.


Screen Buffer - an area of memory that is scanned, decoded and displayed on a screen.
Software - computer programs and data, as opposed to hardware.
Sound Board - The game board that create the game sounds. Contains a 6808 CPU, the sound ROM, a PIA and an audio amplifier. On the Williams games, sounds were not digitized, but created with computer subroutines. <description>
Special Chip - A 4-bit blitter (block transfer) IC used in Robotron and later games (not Defender or Stargate). Two of these are located on the ROM board to off-load some of the graphics chores from the CPU.
Speech Board - A small board that attaches to a sound board and provides a Harris CVSD IC to produce speech.
SRAM - Static RAM. A memory IC that contains semi-permanent data used by a program. SRAM contents can be preserved by batteries when the power is turned off.





Watch Dog - a circuit that resets the CPU if it becomes locked up.
Widget Board - See PIA Board.