Linux boots in 4.76 days on the Intel 4004

Enlarge / A photo of Dmitry Grinberg's custom Linux/4004 circuit board. (credit: Dmitry Grinberg)

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called the Busicom 141-PF, the 4-bit 4004 found limited use in commercial products of the 1970s before being superseded by more powerful Intel chips, such as the 8008 and 8080 that powered early personal computers—and then the 8086 and 8088 that launched the IBM PC era.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