# Booting Linux on the Intel 4004: An Incredible Engineering Achievement
In the realm of hardware tinkering, exploring the outer limits of possibility is a frequent endeavor. Dmitry Grinberg, a prominent figure in hardware hacking, has recently reached an astonishing milestone that merges classic computing with contemporary creativity: **booting Linux on the Intel 4004**, the first commercially produced microprocessor in the world. This accomplishment is not merely a technical wonder but also highlights the adaptability of Linux and the innovation of the maker community.
## The Intel 4004: A Concise Overview
The **Intel 4004**, introduced in 1971, was the inaugural commercially accessible microprocessor. It was initially created for the **Busicom 141-PF**, a Japanese calculator. Featuring just **2,300 transistors** and a clock speed of **740 kHz**, the 4004 represented a significant advancement in computing at that time, but today, it appears remarkably basic. As a **4-bit processor**, it can handle only 4 bits of data simultaneously and possesses extremely limited memory and processing abilities.
Although the 4004 was a monumental advancement in the early 1970s, it was soon overshadowed by more robust Intel processors like the **8008** and **8080**, which became integral to early personal computers. Ultimately, the launch of the **8086** and **8088** processors ushered in the IBM PC era, solidifying Intel’s supremacy in the microprocessor arena. Nowadays, the 4004 is regarded more as a historical relic than as a functional computing device—until now.
## The Obstacle: Executing Linux on a 4004
At first glance, the concept of running **Linux**—a contemporary operating system—on the Intel 4004 appears to be unfeasible. The limited capabilities of the 4004 render it incapable of executing even the most fundamental modern software. Nevertheless, Dmitry Grinberg figured out a method to achieve this, albeit with some ingenious workarounds.
Grinberg’s approach entails utilizing the 4004 to **simulate a MIPS R3000 processor**, the architecture utilized in the **DECstation 2100**, one of the initial platforms to which Linux was ported. By crafting an emulator that operates on the 4004, Grinberg successfully booted a minimized version of **Debian Linux** to a command line.
While the 4004 itself is far too restricted to run Linux natively, the emulator fills the void by emulating a more capable processor. This technique enables Linux to function, albeit at an extremely reduced speed. In fact, it takes approximately **4.76 days** for the Linux kernel to complete its boot sequence on the 4004.
## Surmounting the Limitations of the 4004
Running Linux on the 4004 necessitated overcoming several formidable challenges:
1. **Insufficient ROM and RAM**: The 4004 has very limited memory, complicating the storage and execution of intricate programs. Grinberg’s emulator employs **lookup tables** and various optimization strategies to get the most out of the constrained resources.
2. **Absence of Interrupts**: The 4004 does not feature hardware interrupts, which are crucial for modern operating systems to efficiently manage multiple tasks. Grinberg had to engineer the emulator to navigate this restriction.
3. **Basic Instruction Set**: The 4004 lacks even fundamental logical operations like AND and OR, which are vital for most computing functions. Grinberg’s emulator counters this shortcoming by leveraging software-based methods to execute these operations.
4. **Low Clock Speed**: Even when the 4004 is **overclocked to 790 kHz**, it remains exceptionally slow by current standards. The emulator is crafted to be as efficient as possible, yet the boot procedure hitherto still spans several days to finalize.
## The Hardware Configuration
To realize the project, Grinberg devised a bespoke circuit board featuring the 4004 alongside several other period-appropriate support chips from Intel’s **MCS-4 chipset**. The board incorporates a **VFD (Vacuum Fluorescent Display)** to present Linux output and can accept input through a serial connection. The entire configuration consumes about **6 watts** of energy.
Grinberg’s circuit board design itself is a masterpiece. He deliberately avoided employing **vias** (connections among different layers of the circuit board) and solely utilized **right-angle traces** to impart a vintage look to the board. The end result is a wall-mountable gadget that gradually processes Linux commands over days or sometimes weeks.
## A Gradual but Captivating Boot Sequence
The boot sequence for Linux on the 4004 is excruciatingly slow. It nearly takes five days for the Linux kernel to thoroughly initialize and reach a command prompt. Nonetheless, for Grinberg and other aficionados of vintage computing, the slow pace is an integral part of
