Chess 0.5 Reborn: Another Mainframe Legend for Your Picochess!
Dirk
Hello emulation & simulation fans of old chess programs,
get ready to take another trip back in time!
I've dusted off a true classic from the digital archives and given it a new home on modern hardware. I'd like to introduce you to Chess 0.5, a faithful UCI port of the legendary 1978 Pascal program by Larry Atkin and Peter W. Frey which is more or less a close relative to the legend Chess 4.6
The History: A Trip Back to 1978
Picture the scene: disco is on the radio, bell-bottoms are in fashion, and the world's strongest chess programs are running on colossal mainframe computers the size of a small car. In this era, Larry Atkin was a giant, co-author of the dominant Northwestern University "Chess" series. At the time, the mighty Chess 4.6 was battling for computer chess supremacy.
So, what was Chess 0.5? Think of it as Chess 4.6's brilliant little brother. Written in a dialect of Pascal for the powerful CDC 6600 mainframe, it wasn't designed to be the world champion. Instead, it was a didactic masterpiece published in Byte Magazine. Its purpose was to teach the core principles of computer chess and likely served as a clean, elegant testbed for analyzing ideas that would power its bigger, more complex siblings. It was a "brute-force" engine in the purest sense, with a beautifully simple evaluation function and a raw, non-recursive alpha-beta search.
The Rebirth: From Pascal to Python
We've performed a bit of digital archaeology to resurrect this piece of history. The original Pascal code, with all its quirks and GOTO statements, has been painstakingly ported into a modern Python UCI engine.
Here’s what makes our version tick:
- Python Core: The entire logic has been translated into clean, readable Python.
- python-chess Life Support: We use the rock-solid python-chess library (v1.6 compatible) as a "chassis" to handle the boring stuff like move validation and board mechanics. This lets our engine focus on what makes it unique: its original 1978 brain.
- Full UCI Wrapper: A multi-threaded UCI wrapper ensures the engine communicates flawlessly with modern GUIs like Picochess. It supports stop, ponder, and continuous info updates, just as you'd expect from a modern engine.
Key Features: Your Own Personal Chess Time Machine!
This isn't just a port; it's an interactive museum piece. We’ve exposed the original's core logic through UCI parameters, giving you full control over its brain.
- The "History Switch" (UsePST parameter): This is the coolest feature!
- UsePST = true (Default): The engine is enhanced with modern "Piece-Square Tables," giving it basic positional understanding (e.g., "knights on the rim are dim"). It will play much more reasonable chess.
- UsePST = false: Turn this off to experience the pure, unfiltered 1978 engine! Watch in awe (and sometimes horror) as it plays moves like h3 in the opening, completely blind to long-term strategy but ruthlessly calculating tactics within its short horizon. It’s a fantastic way to feel like a tactical genius!
- The "Thinking Power" Dial (FNODEL parameter): Forget abstract "difficulty levels." Like in the old days, you control the engine's strength by setting its Function NODE Limit.
- FNODEL = 5000: A weak, blitz-happy opponent.
- FNODEL = 500,000: Unleash the full (for its time) computational power of the CDC mainframe on your tiny device!
What to Expect:
Don't expect it to challenge Stockfish. Do expect it to play a fascinating, sometimes head-scratchingly weird, but historically authentic game of chess. It’s a window into the very soul of computer chess's pioneering days.
Enjoy this trip back in time, and may your pawns march ever forward (preferably towards the center)
Sources:
https://www.chessprogramming.org/Chess_0.5
Picochess UCI engine Port:
just put the python script into the engines/script_engiines folder and the executable bash script together with its uci file into the aarch64/script folder.
favorites.ini/engines.ini entry:
[script/chess05]
name = Chess 0.5 by Peter Frey und Larry Atkin (1978)
small = chess05
medium = chess05
large = Chess 0.5
web = Chess 0.5 1978 (Frey, Atkin)
elo = 1200
ponder/brain = n
Enjoy
Dirk