Editing Defender (1981 video game) (section)

=== Hardware ===
The game features amplified [[monaural]] sound and [[Raster graphics|pixel graphics]] on a [[Cathode-ray tube|CRT monitor]]. A [[Motorola 6809]] [[central processing unit]] handles the graphics and gameplay, while a [[Motorola 6800]] microprocessor handles the audio.<ref name="KLOV">{{cite web| url = http://www.klov.com/game_detail.php?game_id=7547| title = Defender - Videogame by Williams (1980)| publisher = [[Killer List of Videogames]]| access-date = 2009-12-06}}</ref> A pack of three [[AA battery|AA batteries]] provide power to save the game's settings and high scores when the machine is unplugged from an electrical outlet. The cabinet artwork is stenciled on the wooden frame.<ref name="PriceGuide-1">{{cite book| title = Official Price Guide to Classic Video Games| first = David| last = Ellis| pages = [https://archive.org/details/officialpricegui00davi/page/337 337–340]| chapter = Arcade Classics| publisher = [[Random House]]| isbn = 0-375-72038-3| year = 2004| chapter-url = https://archive.org/details/officialpricegui00davi| url = https://archive.org/details/officialpricegui00davi/page/337}}</ref>

Development started by focusing on the game's hardware. The staff first debated what type of monitor to use: black-and-white or color. They reasoned that using advanced technology would better establish them as good designers and chose a color monitor. The developers estimated that the game would require 4&nbsp;colors, but instead chose hardware that could display each pixel in 16&nbsp;colors. At the time, the designers believed that was more than they would ever need for a game.<ref name="Ultimate"/> The monitor's resolution is 320×256, an expansion from the then-industry standard of 256×256. The staff believed that the wider screen provided a better aspect ratio and would improve the game's presentation.<ref name="RG-55">{{cite magazine|magazine= [[Retro Gamer]]| publisher = [[Imagine Publishing]]| title = The Making of Defender| issue = 55| pages = 34–39|date=October 2008}}</ref> Video games at the time relied on hardware to animate graphics, but the developers decided to use software to handle animation and programmed the game in [[assembly language]].<ref name="Halcyon"/><ref name="RG-55"/> The switch allowed them to display more on-screen objects at a lower cost.<ref name="RG-55"/>

The game's control scheme uses a two-way joystick and five buttons. Jarvis designed the controls to emulate both ''Space Invaders'' and ''Asteroids'' simultaneously. The player's left hand manipulates the joystick similar to ''Space Invaders'' and the right hand pushes buttons similar to ''Asteroids''. The button functions to shoot projectiles and accelerate use a similar layout to ''Asteroids''. Jarvis reasoned that players were accustomed to the control schemes of past games and felt altering past designs would prove difficult for them.<ref name="RG-55"/>