Book “Anatomy of the 4040 Disk Drive” by Hilaire Gagne

Hilaire Gagne: Anatomy of the 4040 Disk Drive

(HTML, 632K)

This book provides a complete description of the Commodore 4040 dual floppy drive. The book covers file management, data management disk management, file organization, advanced disk programming, hardware and software interfacing, RAM and ROM disassembly, and application examples.

The book contains a full commented disassembly of “CBM DOS V2.1” for the 4040. (The original source is available at

It was written with an unknown word processor, probably on a Commodore PET, and the original files were part of the estate of Dennis Jarvis.

The conversion tool and the HTML are tracked in a git repository.

3 thoughts on “Book “Anatomy of the 4040 Disk Drive” by Hilaire Gagne”

  1. Never figured I’d see this book in circulation on the web; brings back memories of the late nights I’d spend disassembling the code and documenting it. I used my CBM PET 4032 /w an 80 column video mod and printed the book on CBM Daisy Wheel printer (model escapes me now) which drove my parents crazy as they were noisy.



  2. Yes, those files look like WordPro. I remember those to be in screen codes, and have two-letter commands on lines with some prefix character (the checkmark?). Much like, as I later learned, like runoff/nroff etc.

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