A free 512-byte boot-sector program, bootgpt, boots a PC straight into a neural network that dreams fake Linux logs

Chris, built from glowing text-mode block shading, leans close to an old beige computer monitor full of scrolling lines — Illustration: LockerGnome

The output looks right from across the room. Timestamps in brackets, PCI addresses, memory ranges, ACPI interrupt links, the line about registering protocol family 16. Lean in and it falls apart into words like “ryndrde” and “usbbore.” The README calls it a machine that “wakes up and dreams a Linux boot log: timestamps, PCI bars, ACPI events for hardware that never existed.”

Why it matters

The whole engine fits where a PC looks first. A BIOS reads one 512-byte sector off the disk and jumps into it, and two of those bytes are a signature. bootgpt’s author put the inference loop, the disk reads and the screen output in the other 510. “The boot sector is code only,” the README says. “Strings, weights and the vocab table all live in the data sectors, it was the only way to fit inference plus BIOS plumbing into 510 bytes.”

The math was bent to fit the chip. Everything in the model is squeezed to 8-bit integers with power-of-two scales, “so the boot sector can do the whole forward pass with imul and a single idiv.” That’s a 386’s own multiply and divide instructions doing the work a graphics card does for a big model.

It proves its own output. The training script simulates the exact integer math the assembly runs, random-number generator included, so the Python version and the boot sector can be compared side by side. “They match char for char.”

The model is small on purpose. It’s a character-level net with eight characters of context and one hidden layer, trained on 3 MB of fake boot logs that a script generates. The generator keeps one kernel version and one disk per session, “because real boot logs repeat themselves and that repetition is what makes a tiny model look sane.” It does one job, and that job is pretending to be the machine it’s running on.

The developer, Semyon Usachev, posts on X as krlntn, and the repo links his build thread.

@krlntn's post on X

Running it takes four commands on a Mac: install nasm and QEMU with Homebrew, set up a Python environment with numpy, then ./build.sh and ./run.sh. The disk image it makes “is a normal boot image,” and the README says you can write it to a USB stick and boot any BIOS machine with it. “It only reads its own sectors.” Any keypress reboots.

Boot sectors have a long line of these stunts, and the README credits them. Oscar Toledo fit chess, a whole operating system and a BASIC interpreter into 512 bytes. The closest relative is sectorllm, which boots a real five-layer llama2 transformer from about 1.2 KB of real-mode assembly. bootgpt went the other way, with a smaller engine and a model that knows exactly one thing.

Steal this

Try it in QEMU first, and only write it to a USB stick for a machine you’re happy to reboot into it. The image only reads its own sectors, but whatever disk you dd it onto gets overwritten. This is like a demo cartridge: it plays fine in the console, but you don’t record it over your saved game.
When something tiny has to look smart, train it on output that repeats. bootgpt’s fake logs keep one kernel and one disk per boot because repetition is what lets an 11.5 KB model look sane. Kind of like a parrot that only ever hears one phrase: it’ll say that phrase perfectly.
If you rewrite code for a smaller machine, make the big version simulate the small one and diff them. bootgpt’s Python matches the boot sector character for character, so any bug shows up as the first character that differs. This is like proofing a translation by translating it back: wherever it drifts, that’s your mistake.

The README sets the bar plainly: with eight characters of context and one hidden layer, the sample log “is roughly the quality you get.” What it doesn’t say is how much better the dream gets with a sixteenth character, or whether 510 bytes has any room left to find out.

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A free 512-byte boot-sector program, bootgpt, boots a PC straight into a neural network that dreams fake Linux logs

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