Bas Smits spent over three years writing “Game Engine White Papers: Commander Keen” - a 214-page, full-color book about how games were made in the late 1980s and early 1990s, more than 35 years after the original. Available as a free PDF or as a printed book on Amazon.

The book covers hardware (80286, EGA video cards, sound cards, keyboards), game assets, the engine architecture, and how the CGA version of the game was created. Source code for the book project is on GitHub.

It took me over three years to complete the book, and the entire experience was immensely rewarding. It felt like returning to my early teenage years, debugging and experimenting with C and assembly code on a MS-DOS computer.

The 214-page, full-color book explains in great detail what it was like to develop games in the late eighties and early nineties. Topics include hardware (80286, EGA video cards, sound cards, keyboards, and more), game assets, the engine itself, and even the creation of the CGA version of the game.

Source: forgottenbytes.net