There are various ways to implement an Intel i386 CPU on an FPGA, with one of the most fascinating methods being the use of original microcode. A great example of this is the z386 project by nand2mario, which details its current progress.
This project builds on previous work like the z8086 project, designed for the Intel 8086 CPU. By running the original microcode, z386 aims for a close match with the original hardware. However, the complexity between the 8086 and 80386 is quite significant.
The instruction set is larger, and the internal state is more complicated. It incorporates advanced features like memory management, paging, and debugging for registers, alongside protected mode capabilities introduced with the i286.
Currently, z386 operates on several FPGAs, including the Altera Cyclone V and Gowin GW5A. Its performance equals roughly a 70 MHz i386, though it may be slightly less efficient due to a smaller 16 kB cache compared to the 32+ kB cache in some faster i386 CPUs. Still, it’s capable of running various software, including classic games like DOOM.
Interestingly, the aim of z386 isn’t to outperform existing cores, such as ao486. Instead, it serves as an archaeological look into how the original hardware worked with its microcode. This kind of project reminds us how far technology has come and the foundational role older CPUs play in today’s computing landscape.
For those interested in computer architecture, projects like these highlight the historical value of past technology and showcase how we can preserve and understand it through modern tools.
