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A 80386 Master/Slavev S100 bus CPU board + RAM


Experienced Member
Oct 19, 2008
San Ramon, CA
Well it looks like it's finally done. After some 6 prototype boards and one year later it looks like we now have a completely functional S100 bus 80386 board. This board runs on a 21 slot motherboard at 9MHz for all interrupts, I/O ports and RAM from 0 to 16MB. For the remaining RAM (up to 4GB for the 80386) the CPU runs at 36MHz (in pipeline protected mode) and 32 bits wide via two above board cable connectors.

A complete description of the board can be found here:-


There is also a short video of the board in operation towards the bottom of the page.

A major component of this effort was writing the 80386 monitor. It's in fact surprising how little example code there is out the demonstrating the setting up the 80386 to switch from real to protected mode. This is written up here:-


The board currently works with two static RAM boards that sit in the bus but communicate directly (and only) with the 80386. The capacity of these boards are 8 and 32 MB's. These are described here:-



A big thanks goes out to Andrew Lynch at N8VEM (http://n8vem-sbc.pbworks.com/w/page/4200908/FrontPage) for laying out the many prototypes these boards took. Thanks Andrew.

I will be ordering a few "commercial quality" boards for myself. If anybody else would like one of these boards they can let me know. However be aware that these boards are not only complex but expensive to build. The boards themselves are the smallest part of the whole equation. The 8MB static RAM board is a rock solid board and great for testing out the hardware and software but those Alliance Memory Inc. 512x8 static RAM chips cost about $20 each. The 32MB board on the other hand has 4 times the capacity for about the same price but uses SMD chips.

Next up is an 80486 board and the real challenge a 4GB DRAM board!


John Monahan


Experienced Member
Dec 26, 2012
There is also a short video of the board in operation towards the bottom of the page.

John Monahan

This is amazing! I am sad that there are not more videos of the board in action. Could you run Wolfenstein 3D on this thing? How about Windows 95? Even a Linux GUI would be sweet. All that work - and so humble as to not show any bragging rights videos. I mean - who has ever run Wolf 3D on an S-100 based system! Wish I had the tech know-how to get into S-100's.