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An 8086 Bios for S-100 systems to run MS-DOS/FreeDOS


Experienced Member
Oct 19, 2008
San Ramon, CA
I have been writing 8086 code for a fairly comprehensive 8086 monitor (~9000 lines of code) that with a number of new S-100 boards (an 8086 board, our IDE Board, our ZFDC board , our PIC-RTC Board and the Propeller driven Console IO board) allows one to boot MS-DOS. The goal is to have hardware and a BIOS so that standard generic MS-DOS (or FreeDOS) does not know it's not talking to a PC motherboard. This turned out to be more difficult than I thought. Most major PC software interrupts (0-20H) have to be emulated in very precise ways. Anyway delighted to say MS-DOS (V4.01) now boots up on 3.5" floppies or on a CF-Card with our IDE drive S-100 board.

If you have time take a look at
http://s100computers.com/Software Folder/8086 Monitor/8086 Monitor.htm
there are a few short videos there that show the system in action.

Except for the 8086 board the other boards are already done. The 8086 prototype has been working here for months (8MHz) and Andrew expects the "commercial quality" board with trace optimization to go out fairly