Prof. Dr. rer. nat. Peer Johannsen

Weird Science - Tales from the Vectrex Academy Lab

Vectrex Performance Experiment


Project Status

  • Playable alpha prototype, version 0.2


  • A simple one or two player chess-like game with some basic AI
  • Intended to be rather an academic experiment than the attempt to create a good Vectrex chess game


  • The goal of this experiment is to keep the complete board drawn at a 50Hz framerate at all times.
  • Especially, the board shall remain visible during the AI move computations.
  • Only the original Vectrex hardware is used, no additional RAM, no "stronger" external CPU.
  • The code is pure Vectrex C, using the BIOS routines for interfacing with the console hardware only.
  • Also, the code does not use processor interrupts.

How To Play

  • The rules of Kingslayer Chess are a simplified and modified version of the common rules of chess.
  • The goal of the game is to explicitly slay the opponent's king (hence the name).
  • In order to win the game, the king must be taken by an attacking move of another piece.
  • There is no checking-rule, and the game only ends if the king is taken.
  • There is no castling, en-passant, or pawn-promotion. Also no 50-moves-rule or alike.
  • Use the joystick and the buttons of controller 1 to play the game.

Known Issues and Current Limitations

  • The are currently three different types of AI (implementing levels 1 to 3 of the minimax algorithm).
  • Also, a non-AI can be chosen as opponent which does completely random moves only.
  • The screen size of the chess board is the (currently) best possible compromise between performance and the goal to display the board at any time while maintaining a 50Hz frame rate.
  • The code of the core AI has not yet been optimized for performance, and thus the 50Hz frame rate goal is still being slightly exceeded every once in a while. This will be addressed soon.
  • The AIs are certainly not club player level and rather intended as (worthy?) opponents for the casual novice or amateur player. Maybe they can also provide some fun for beginners or kids who are just about to start learning chess.
  • As of now, the order of "thinking" time of AI 1 is approx 1 second per move, AI 2 needs between 6 and 30 seconds, and AI 3 on average computes its moves in the range from 30 seconds to 3.5 minutes, occasionally taking up to 7 minutes.
  • It is sort of fun to watch the AIs play against each other...


  • Peer Johannsen

Prototype Screenshots

Prototype 0.1 Demo Video

Additional Links


  • Downloads are free and for non commercial use only. Use at your own risk.
  • Please respect the copyright and credit the author and the origin of this game.


Latest modification on 06/04/2021, 15:30

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