Revving Up the Past: Linux on the Intel 4004

In a remarkable feat of engineering and innovation, hardware hacker Dmitry Grinberg has successfully booted Linux on the Intel 4004, the world's first commercial microprocessor. Released in 1971, the 4-bit 4004 had only 2,300 transistors and an original clock speed of 740 kHz, making it extremely primitive compared to modern standards. But Grinberg's achievement is not just about booting Linux, it's about pushing the limits of what's possible with 1970s technology. Grinberg didn't try to run Linux directly on the 4004, which is far too limited. Instead, he created an emulator that runs on the 4004 and emulates a MIPS R3000 processor, the architecture used in the DECstation 2100 workstation that Linux was originally ported to. This emulator, along with minimal hardware emulation, allows a stripped-down Debian Linux to boot to a command prompt.To make this feat possible, Grinberg had to overcome numerous challenges. The 4004 has extremely limited ROM and RAM, no interrupts, and lacks even basic logical operations like AND and OR. Grinberg's emulator makes clever use of lookup tables and other tricks to squeeze maximum performance out of the primitive CPU. The final hardware uses the 4004 (overclocked to 790 kHz) along with several other period-correct support chips from Intel's MCS-4 chipset. It includes a VFD display to show Linux output and can accept input over a serial connection. The whole setup draws about 6 W of power. Grinberg designed a custom circuit board with no vias and only right-angle traces for a retro aesthetic. It's meant to be wall-mountable as an art piece, slowly executing Linux commands over the course of days or weeks. While it has no practical purpose, the Linux/4004 project demonstrates the flexibility of Linux and pushes emulation to its limits. Grinberg is considering the possibility of offering kits or fully assembled boards for others who want to experience Linux at its slowest, though this is not yet definite.