Developer Creates x86 CPU Emulator Entirely in CSS - No JavaScript Required

In a remarkable demonstration of pushing web technologies to their limits, developer Lyra Rebane has created an x86 CPU emulator written entirely in CSS - with no JavaScript, WebAssembly, or any other traditional programming language involved.

According to the project announcement on Twitter, the emulator includes a basic display and keypad interface, along with several preinstalled programs that can calculate the Fibonacci sequence, generate Pascal's triangle, and run a variation of Wordle. The project showcases how modern CSS implementations have evolved far beyond their original styling purposes.

Technical Requirements and Limitations

The emulator requires a recent version of a Chromium-based browser to function properly, as Rebane utilized some CSS features that aren't yet standardized across all browsers. This dependency highlights the cutting-edge nature of the techniques employed in the project.

For developers interested in creating their own programs for the emulator, Rebane has documented the process of compiling C code using the gcc-ia16 compiler. This toolchain allows developers to write programs in C, compile them to x86 machine code, and then run them within the CSS-based environment.

What It Can and Cannot Do

While the emulator implements most x86 assembly instructions, it notably lacks several critical features required for running more complex applications. Specifically, it's missing interrupt handling, port input/output functionality, and block-operation instructions. These limitations mean that popular applications like Doom cannot run on the emulator - at least not yet.

The inability to run Doom stems from multiple factors beyond just missing instructions. Doom is a 32-bit program that requires an 80386 or higher CPU, 4 MB of RAM, and the ability to enter protected mode - capabilities that the current CSS emulator doesn't provide.

The Creative Process

What makes this project particularly impressive is that Rebane completed it without any AI assistance or "vibe-coding." As she points out, the unconventional thinking required to transform CSS into a state machine capable of emulating a CPU would have been difficult for AI tools to generate, given the novel approach required.

Rebane credits Jane Ori's CSS CPU Hack as instrumental inspiration for her own ideas, demonstrating how the developer community builds upon each other's creative explorations of technology boundaries.

Implications and Reactions

This project has sparked interesting discussions about the nature of programming languages and the computational capabilities of CSS. Many developers have long joked about whether HTML and CSS qualify as "real" programming languages, and this project provides a definitive answer - CSS can indeed perform complex computational tasks when pushed to its limits.

Some commenters have raised questions about whether this could represent a new attack vector, given CSS's newfound computational capabilities. However, Rebane notes that an attacker would first need to create the machine environment itself, making this scenario unlikely in practical security contexts.

Why Build This?

When asked about the purpose or utility of the project, Rebane simply stated it was a "fun project." This response encapsulates the spirit of many groundbreaking technical demonstrations - sometimes the most valuable innovations come from pure curiosity and the desire to explore what's possible, rather than from solving immediate practical problems.

The project serves as a fascinating example of how modern web technologies continue to evolve in unexpected ways, challenging our assumptions about what different languages and tools can accomplish.