A 32-Bit 386 PC on a Breadboard

A favorite pastime of retro computing and computer engineering hobbyists involves getting vintage CPUs up and running from scratch. Whether it is a 6502, Z80, or an early Intel chip, this is an excellent way to learn more about how computers work while having some fun in the process.

Most commonly, the process starts by free-running the chip on a breadboard. Once the signals have all been sorted out, memory and peripherals can be added to make a complete computer. Just add a little at a time, and you’ll eventually have your own complete custom retro computer.

However, this tried-and-true formula starts to break down as CPUs become more advanced. Consider the Intel 80386 chip that YouTuber Breadboarding Labs has been working with, for instance. Instead of the 40 or so pins earlier processors like the 6502 CPU had, the 386 has 132 pins. These chips aren’t in a nice, breadboard-friendly DIP package either. Furthermore, when you consider the higher clock speeds a 386 runs at, it starts looking like a disaster waiting to happen.

That hasn’t stopped Breadboarding Labs, though. In a new video series, the creator sets out to build a fully functional 32-bit PC around an Intel 386 DX-33 — entirely on breadboards. To make the project feasible, the CPU will be significantly underclocked to 8 MHz, helping maintain signal integrity across a sprawling setup that spans more than two dozen interconnected breadboards. An adapter will also be built to break the pins out for a breadboard.

The system design draws inspiration from several classic machines, including the IBM PC-XT, PC-AT, and especially the Compaq DeskPro 386. By blending elements from these systems, the build aims to strike a balance between historical accuracy and practical reliability. A dedicated 32-bit memory bus allows the CPU to interface with 2 MB of SRAM arranged in a full 32-bit configuration, while a 16-bit ISA bus extension provides compatibility with expansion hardware.

Handling the complexity of a 386 system requires more than just careful wiring. Instead of relying on dozens of discrete logic chips, the project uses programmable logic devices like ATF16V8 and 20V8 PLDs to manage address decoding and bus control. Fast 74F-series logic chips are also used for buffering, ensuring the system can meet the tighter timing requirements of the 386 architecture.

The build incorporates classic PC components as well, including dual 8259A interrupt controllers and dual 8237 DMA controllers to handle data transfers efficiently. An 8042-compatible controller provides PS/2 keyboard and mouse support, bringing the system closer to a usable personal computer.

One particularly clever feature that was implemented is BIOS shadowing, where code from slower ROM is copied into faster RAM at startup to improve performance. Additional touches, like a fail-safe timer and variable speed control, allow the machine to slow down to XT-era speeds for compatibility with older software.

This project is still in the early stages, so be sure to check back in for the latest updates. Even if you aren’t building your own 386 breadboard computer, you’ll learn a lot from the videos.