M8SBC-486 (Homebrew 486 computer)

Summary

M8SBC-486 (Homebrew 486 computer) [Back to the homebrew computers page] The M8SBC-486 is a 486 homebrew computer motherboard made from scratch. From the schematic and PCB to the chipset! It is not based on existing designs, but rather on my experience with my previous experimental 486 homebrew (page about it coming soon!). 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 DOOM. However, my design choices made it compatible enough to run other cool stuff! I call it "kinda PC compatible" because it has a lot in common with standard older x86 PCs. The main things missing here are the secondary PIC and DMA. However, based on my tests on this board, many programs can work without these. The missing DMA especially removes sound card support. Just see below the compatibility table! GitHub repository of the project: https://github.com/maniekx86/M8SBC-486 TheRetroWeb entry (thanks!): https://theretroweb.com/motherboards/s/maniek86-m8sbc-486 Page / subpages last updated: 14/01/2026 (Quite a bit may not yet be described, as I was making "dev blogs" in a forum channel on a particular Discord server. I am slowly working to write it all down here.) Specs: 150*150mm 4 layer PCB. Custom holes placement! PGA-168 socket for 5V 486 CPUs. FSB currently runs at 24 MHz meaning that DX2 CPUs work at 48 MHz Currently operating at 24 MHz FSB Xilinx Spartan II XC2S100 FPGA as the chipset. Codename "Hamster 1" 4 MB of SRAM 256 KB (224 KB accessible) ROM for BIOS 8254 Programmable Interval Timer (PIT) 8259 Programmable Interrupt Controller (PIC) Two 16-bit ISA slots PS/2 Keyboard port. Controller is implemented in the FPGA Simple CMOS RTC and CMOS storage. Implemented in the FPGA too ATMega128 as reset circuit handler, nonvolatile CMOS storage and bitstream loader. As this project is pretty big and took me much more time than my previous homebr...