PiDP-8/I Software

CHEKMO II: Chess Playing Program
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Originally distributed as DECUS 8-822

Upstream source: Vince Slyngstad's so-much-stuff repository offers the archival DECUS 8-882 source and a PDF scan of the documentation (provided here as decus-8-882.pdf).

However, a slightly modified source can be found in a DECtape image on Dave Gesswein's It has a small patch and enables the OS8 config by default. That is the source of CHEKMO.PA provided here.

There is also a cool writeup with links to other interesting content at

Original Decus Writeup:

Author: John E. Comeau Digital Equipment Corporation Maynard, MA

Operating System: Paper Tape

Source Language: PAL-8

Memory Required: 4K

Other Software Required: Requires OS/8 for assembly.

Abstract: CHEKMO II is a chess playing program which will run on any PDP-8 family computer. The program will play either the white pieces or the black pieces, and will play and accept all classes of legal moves, including castling both short and long, en passant pawn captures, and pawn promoting moves to any legal promotion piece. The program prints out its moves m Algebraic Notation, and accepts moves using Algebraic Notation.

Included in the command structure of the program are commands which allow you to input board positions using Forsyth Notation, and get a printout of the board at your terminal.

Media Price Code: A2, F6, H32, K27 Format: OS/8 Catalog: August 1978