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Turbo Pascal 3.02A， deconstructed
!Image 3: Simon Willison's Weblog Simon Willison's Weblog @Simon Willison
One Sentence Summary
Simon Willison demonstrates how to use Claude to deconstruct the legendary 40KB Turbo Pascal 3.02A binary into an interactive, annotated memory map and assembly visualization.
Summary
This article explores the remarkable efficiency of Borland's 1985 Turbo Pascal 3.02A, which managed to fit a full text editor, IDE, and Pascal compiler into a single 39,731-byte executable. Inspired by the 'Things That Turbo Pascal is Smaller Than' list, the author utilizes Claude (LLM) to perform binary analysis and reverse engineering on the freeware executable. The result is an interactive web artifact that maps the binary's memory segments, decompiles them into assembly, and provides human-readable annotations. The post also shares the specific prompt sequence used to guide the AI through the deconstruction process, showcasing a novel application for AI in software archeology.
Main Points
* 1. Turbo Pascal 3.02A represents a pinnacle of software optimization and density.The executable's ability to house a complete development environment in under 40KB serves as a stark contrast to modern software bloat and a masterclass in efficient engineering. * 2. Modern LLMs are capable of sophisticated binary deconstruction and visualization.By providing the binary file and structured prompts, the author demonstrates that AI can identify code segments, decompile assembly, and reconstruct logic with high accuracy. * 3. Interactive artifacts enhance the understanding of low-level legacy software architecture.Mapping raw binary data into labeled segments like the Pascal Parser, x86 Code Generator, and File I/O system makes complex 1980s engineering accessible to modern developers.
Metadata
AI Score
78
Website simonwillison.net
Published At Yesterday
Length 183 words (about 1 min)
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20th March 2026 - Link Blog Turbo Pascal 3.02A, deconstructed. In Things That Turbo Pascal is Smaller Than James Hague lists things (from 2011) that are larger in size than Borland's 1985 Turbo Pascal 3.02 executable - a 39,731 byte file that somehow included a full text editor IDE and Pascal compiler.
This inspired me to track down a copy of that executable (available as freeware since 2000) and see if Claude could interpret the binary and decompile it for me.
It did a great job, so I had it create this interactive artifact illustrating the result. Here's the sequence of prompts I used (in regular claude.ai chat, not Claude Code):
> Read this https://prog21.dadgum.com/116.html > > > Now find a copy of that binary online > > > Explore this (_I attached the zip file_) > > > Build an artifact - no react - that embeds the full turbo.com binary and displays it in a way that helps understand it - broke into labeled segments for different parts of the application, decompiled to visible source code (I guess assembly?) and with that assembly then reconstructed into readable code with extensive annotations
!Image 5: Simon Willison's Weblog Simon Willison's Weblog @Simon Willison
One Sentence Summary
Simon Willison demonstrates how to use Claude to deconstruct the legendary 40KB Turbo Pascal 3.02A binary into an interactive, annotated memory map and assembly visualization.
Summary
This article explores the remarkable efficiency of Borland's 1985 Turbo Pascal 3.02A, which managed to fit a full text editor, IDE, and Pascal compiler into a single 39,731-byte executable. Inspired by the 'Things That Turbo Pascal is Smaller Than' list, the author utilizes Claude (LLM) to perform binary analysis and reverse engineering on the freeware executable. The result is an interactive web artifact that maps the binary's memory segments, decompiles them into assembly, and provides human-readable annotations. The post also shares the specific prompt sequence used to guide the AI through the deconstruction process, showcasing a novel application for AI in software archeology.
Main Points
* 1. Turbo Pascal 3.02A represents a pinnacle of software optimization and density.
The executable's ability to house a complete development environment in under 40KB serves as a stark contrast to modern software bloat and a masterclass in efficient engineering.
* 2. Modern LLMs are capable of sophisticated binary deconstruction and visualization.
By providing the binary file and structured prompts, the author demonstrates that AI can identify code segments, decompile assembly, and reconstruct logic with high accuracy.
* 3. Interactive artifacts enhance the understanding of low-level legacy software architecture.
Mapping raw binary data into labeled segments like the Pascal Parser, x86 Code Generator, and File I/O system makes complex 1980s engineering accessible to modern developers.
Key Quotes
* A 39,731 byte file that somehow included a full text editor IDE and Pascal compiler. * I had it create this interactive artifact illustrating the result. * Build an artifact... that embeds the full turbo.com binary and displays it in a way that helps understand it. * It did a great job, so I had it create this interactive artifact illustrating the result.
AI Score
78
Website simonwillison.net
Published At Yesterday
Length 183 words (about 1 min)
Tags
Turbo Pascal
Reverse Engineering
Claude AI
Binary Analysis
Retro Computing
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