A hacker booted Linux on Intel's 4004 from 1971 — the boot takes 4.76 days

The Intel 4004, the world's first commercial microprocessor, was designed in 1971 for the Busicom 141-PF calculator: 2,300 transistors, 4-bit, 740 kHz, no interrupts, and not even basic logical operations like AND and OR. Hardware hacker Dmitry Grinberg — who in 2012 set the record for running real Linux on the lowest-end machine ever, an 8-bit AVR microcontroller, and had since been overtaken — decided to push the record to the very first microprocessor.

The trick is an emulator inside the impossible machine: the 4004 runs an emulator of the MIPS R3000, the architecture of the DECstation 2100 workstation that Linux was originally ported to. Lookup tables and other tricks squeeze performance out of the primitive CPU; the final build overclocks the 4004 to 790 kHz, surrounds it with period-correct Intel MCS-4 support chips, shows Linux output on a VFD display and takes serial input, all at about 6W. A stripped-down Debian Linux boots to a command prompt in 4.76 days and can execute commands over days or weeks.

The custom circuit board — no vias, right-angle traces only, wall-mountable as an art piece — has no practical purpose, but the full schematics and source are published on Grinberg's site, and he has considered offering kits for people who want to experience Linux at its slowest.

The problem is recast as emulation: instead of squeezing Linux into 2,300 transistors, give the 4004 a software machine it can run Linux on.

The emulated target is chosen for lineage — the MIPS R3000 of the DECstation 2100, the exact machine Linux was first ported to.

Lookup tables substitute for the logic operations the silicon physically lacks, the kind of constraint-driven trick that makes the feat possible at all.

It is verifiable to the last detail: schematics and source are public, and the boot is measurable — 4.76 days.

When a platform can't run the software, wrap the gap in an emulation layer aimed at the software's original home — one slow machine impersonating the machine the code expects.

Ars Technica covered the project in September 2024 as a demonstration of Linux's flexibility and the limits of emulation; Grinberg has floated selling kits or assembled boards, but nothing was committed in the source. His earlier 2012 AVR record had been surpassed by others, which is what set this project in motion.