Piotr Grzesik's M8SBC-486 Is a Brand-New Motherboard for Vintage Intel 486 Chips — And It Runs Doom

Electronics student and vintage computing enthusiast Piotr Grzesik has designed an open source motherboard designed to play host to an Intel 486 processor — originally launched in 1989, and replacing now long-discontinued parts with soft-core equivalents running on an FPGA.

"The M8SBC-486 is a 486 homebrew computer motherboard made from scratch — from the schematic and PCB to the chipset," Grzesik explains. "It is not based on existing designs, but rather on my experience with my previous experimental 486 homebrew. I started working on it back in August 2025 and I started researching the 486 CPU in April 2025. I initially planned to make it just a 486 homebrew with the ordinary goal of getting it to run Linux and [id Software's] Doom. However, my design choices made it compatible enough to run other cool stuff!"

The i486, more commonly known as the 486, was Intel's fourth-generation in the x86 family. Launched in 1989, the 486 offered full compatibility with Intel's earlier i386, 80286, and 8086, but with a major boost to performance — and entered the history books as the first x86 part to feature more than a million transistors. While the part may not have been formally discontinued until 2007, though, getting your hands on a working motherboard for one can be a challenge — but perhaps not as big a challenge as building one from scratch.

The M8SBC-486 features a PGA-168 socket compatible with 5V 486 CPUs, both from Intel and its various competitors of the era, and runs at a 24MHz front-side bus (FSB) speed — meaning a 24MHz clock speed for standard 486 parts, 48MHz for DX-2 clock-doubled parts, and a theoretical but untested owing to lack-of-5V-variant 72MHz for the clock-tripled DX-4, all slightly short of the 25/33/50/66/75/100MHz speeds available on mass-produced motherboards.

While motherboards of the era used application-specific integrated circuits for their chipset, Grzesik has replaced these long-discontinued chips with an AMD Xilinx Spartan II XC2S100 FPGA running a software chipset codenamed "Hamster." The board includes 4MB of static RAM (SRAM), 256kB of ROM space for the BIOS, both the 8254 Programmable Interval Timer (PIT) and 8259 Programmable Interrupt Controller (PIC), but lacks a secondary PIC and support for direct memory access (DMA). There are two ISA sockets for add-on hardware, and an on-board Microchip ATmega128 microcontroller to handle the reset circuit, CMOS storage, and load bitstreams to the FPGA.

As for what it can do, that's a surprisingly complete list: the lack of DMA means no support soundcards, other than potentially the classic AdLib Music Synthesizer Card, the ISA slots do not support plug-and-play (PnP) cards, network connectivity is untested as is SCSI storage, but it's capable of running both Microsoft's MS-DOS 6.22 and the open source FreeDOS 1.4, Linux 2.2.26, and very nearly Windows 3.1 — "It launches, gets the shell, and is usable with the keyboard," Grzesik notes, "but I can't get [the] mouse to work!" Other tested software known to run on the board includes the Second Reality demo, FastTracker II music tracker, 3DBench 1.0, and — of course — both id Software's Wolfenstein 3D and Doom.

"This project is essentially my hobby, as I like retro, electronics, digital circuits and low-level programming," Grzesik says. "I never expected this computer to run DOS in the first place. I consider it pretty much experimental and made to research the workings of older x86 chips. I am pretty sure that this work could be used to build something more robust and stable or even to develop fully custom-made boards for other x86 CPUs. It took me a lot of time, but I don't regret it. There are still many issues, but it's heartwarming that I can get so much existing software to work."

More information is available on Grzesik's website, while design files and source code available on GitHub under a mixture of the permissive MIT license and the reciprocal GNU General Public License 3.