Back to the Basics: Deconstructing 30-Year-Old GW-BASIC Game Design
Overview
Retrocomputing isn't just about nostalgia; it鈥檚 a masterclass in how much our software design paradigms have shifted. Running code from the early 90s written in reveals a world without modern abstractions. In this era, developers managed hardware directly, ignored separation of concerns, and relied on linear logic that would make a modern engineer shudder. We explore how to revive this 16-bit code and what its structure teaches us about the evolution of programming.
Prerequisites
To follow this historical deep dive, you should understand:
- Legacy Systems: Basic familiarity with and 16-bit executables.
- Virtualization: Knowledge of how to set up a virtual machine environment.
- Programming Logic: Comfort with procedural code and the concept of memory addresses.
Key Libraries & Tools
- : A powerful x86 and AMD64/Intel64 virtualization product used to run legacy operating systems.
- : The target OS for emulation, as it still retains the NTVDM (NT Virtual DOS Machine) capabilities removed from 64-bit Windows.
- : The go-to repository for obtaining legitimate legacy software installers.
Code Walkthrough: Memory and Input
In legacy BASIC, developers often manipulated the environment by hitting memory addresses directly.
10 PEEK(1047)
20 POKE 1047, 64
30 IF ERR THEN GOTO 2710
Line 10 uses PEEK to read the status of memory address 1047, which governed the Num Lock state. Line 20 uses POKE to force that state to 'on,' ensuring the numeric keypad worked for player movement. Without an event-driven system, the code relies on GOTO statements to jump to error-handling blocks or subroutines, creating what we now call 'spaghetti code.'
Syntax Notes: The Lack of State Separation
Modern games separate the Game World State from the Rendering Loop. In this 30-year-old code, those concepts are fused. To detect a collision or a goal, the program used a pixel-color check:
IF POINT(X, Y) = 15 THEN PLAY "CDEFG"
The code literally 'looks' at the color of a pixel on the screen. If it matches the 'Diamond' color, it triggers a sound and awards points. This makes the UI and the logic inseparable.
Tips & Gotchas
- The Sound Trap: In , the
PLAYcommand is blocking. The entire program halts until the melody finishes, meaning no other logic or movement can occur. - 16-bit Limitations: You cannot run these files natively on Windows 10/11. Use with to maintain 16-bit compatibility.
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GW BASIC Games I Wrote When I Was a Kid 馃幃 Running 30 Year Old Code
WatchArjanCodes // 15:37
On this channel, I post videos about programming and software design to help you take your coding skills to the next level. I'm an entrepreneur and a university lecturer in computer science, with more than 20 years of experience in software development and design. If you're a software developer and you want to improve your development skills, and learn more about programming in general, make sure to subscribe for helpful videos. I post a video here every Friday. If you have any suggestion for a topic you'd like me to cover, just leave a comment on any of my videos and I'll take it under consideration. Thanks for watching!