Cyrus IS Chess: Richard Lang's 1981 Classic Reborn as a UCI Engine

[Steve Maughan]

I'm pleased to announce the release of Cyrus IS Chess as a UCI-compatible engine.

For those who don't know its history, Cyrus IS Chess was written by Richard Lang for the ZX Spectrum. It won the 1981 European Microcomputer Chess Championship, and it was the first of Richard's groundbreaking programs. He went on to become World Microcomputer Chess Champion many times over, and his later work shaped dedicated chess computers for a generation.

A bit of nostalgia
This one is personal for me. My very first computer was a 48K ZX Spectrum, hooked up to a 15-inch portable TV in my bedroom, and Cyrus IS Chess was the first decent chess program I ever owned. I still remember being amazed that I had a real chess opponent sitting on my bedroom TV. Bringing it back to life has been a real pleasure.

Not an emulation
It's worth stressing that this is not an emulation. It's a behavioral translation of the original program. The board representation, the search, and the evaluation have all been preserved, which means it plays exactly the same moves as the original. What has changed is the underlying implementation: the original's exact memory layout has been replaced with Zig tables. The result is an engine that is faithful to Lang's play while being far more robust, and it doesn't carry over the bugs of the original.

Platforms
Builds are available for Windows (Intel and ARM), Linux, Android, and macOS.

Download
Cyrus IS Chess on GitHub

I hope you enjoy playing against (or testing) a little piece of computer chess history. If you run into any bugs or problems, please let me know, either here or via the repository.

— Steve

[Essay]

Excellent work Steve.

My first computer chess program was Artic Computing's ZXChess II (by Anthony Adam and/or Chris Thornton) which ran on my Sinclair ZX80/81 with a 16K RAM pack. It played a decent game with upper and lower case letters on an 8x8 checkered board display.
When I bought the Spectrum 48K I purchased Richard Lang's Cyrus IS Chess and found it to be excellent. Later I bought Cyrus IS Chess II and also had Superchess II (by Chris Whittington), the last chess program I bought for the Spectrum was Colossus 4 (by Martin Bryant).
It was remarkable how good these programs were as they ran on an 8 bit Z80A CPU @ 3.5MHz.

I still enjoy playing Richard Lang's ChessGenius 3.1 program on my Android smart phone.