Benj Edwards

– Sep 23, 2024 6:48 pm UTC

Hardware hacker Dmitry Grinberg recently achieved what might sound impossible: booting Linux on the Intel 4004, the world’s first commercial microprocessor. With just 2,300 transistors and an original clock speed of 740 kHz, the 1971 CPU is incredibly primitive by modern standards. And it’s slow—it takes about 4.76 days for the Linux kernel to boot.

Initially designed for a Japanese calculator called the Busicom 141-PF, the 4-bit 4004 found limited use in commercial products of the 1970s before being superseded by more powerful Intel chips, such as the 8008 and 8080 that powered early personal computers—and then the 8086 and 8088 that launched the IBM PC era.

If you’re skeptical that this feat is possible with a raw 4004, you’re right: The 4004 itself is far too limited to run Linux directly. Instead, Grinberg created a solution that is equally impressive: 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.

Grinberg is no stranger to the challenge of implementing Linux on unconventional hardware. He states on his website, “In 2012, I ran real Linux on an 8-bit microcontroller (AVR), achieving a world record for the least powerful machine to ever run Linux.” As technology progressed and others built upon his record, he aimed to reclaim his title by focusing on the very first microprocessor.

To get Linux running on the 4004, Grinberg faced numerous obstacles. The 4004 posseses severely constrained ROM and RAM capacities, lacks interrupts, and does not support basic logical operations such as AND and OR. Using innovative methods, including lookup tables, Grinberg’s emulator maximizes the limited capabilities of this basic CPU.

The ultimate assembly incorporates the overclocked 4004 (at 790 kHz) alongside a variety of authentic support chips from the Intel MCS-4 series. It features a VFD display for Linux feedback and accepts input through a serial connection. The entire system consumes approximately 6 W of power.

To assemble the components, Grinberg crafted a specialized circuit board devoid of vias and employing only right-angle traces to maintain a vintage look. This design is intended for wall mounting, serving not only as a functional piece but also as a piece of art, processing Linux commands over extended periods.

The Linux/4004 project serves as a testament to Linux’s adaptability and the extreme capabilities of emulation, despite being functionally impractical. Grinberg is contemplating whether to make kits or complete boards available for enthusiasts keen to explore the slowest iteration of Linux, though plans are still unconfirmed.

Comprehensive details about this endeavor, including both schematics and the source code, can be found on Grinberg’s website. It offers an intriguing insight for anyone interested in the intersection of vintage computing and advanced Linux configurations, showcasing what can be achieved with 1970s technology combined with innovative engineering.

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