Small Things Retro

486Tang – 486 on a credit-card-sized FPGA board

8086 Microcode Browser

Since releasing 486Tang , I’ve been working on recreating the 8086 with a design that stays as faithful as possible to the original chip. That exploration naturally led me deep into the original 8086 microcode — extracted and disassembled by Andrew Jenner in 2020.

z386: An Open-Source 80386 Built Around Original Microcode

This is the fifth installment of the 80386 series . The FPGA CPU is now far enough along to run real software, and this post is about how it works. z386 is a 386-class CPU built around the original Intel microcode, in the same spirit as z8086 .

80386 Protection

I'm building an 80386-compatible core in SystemVerilog and blogging the process. In the previous post , we looked at how the 386 reuses one barrel shifter for all shift and rotate instructions. This time we move from real mode to protected and talk about protection .

80386 Memory Pipeline

The FPGA 386 core I've been building now boots DOS, runs applications like Norton Commander, and plays games like Doom. On DE10-Nano it currently runs at 75 MHz. With the core now far enough along to run real software, this seems like a good point to step back and look at one of the 80386's performance-critical…

80386 Multiplication and Division

When Intel released the 80386 in October 1985, it marked a watershed moment for personal computing. The 386 was the first 32-bit x86 processor, increasing the register width from 16 to 32 bits and vastly expanding the address space compared to its predecessors. This wasn't just an incremental upgrade—it was the…