Two homebrew S100 systems, TRS-80 Model III compatible

Two old and remarkable machines, but no idea of the dates when they were built.

They are complete implementations of a Model III TRS-80 in homebuilt S-100 chassis, using a combination of homebuilt and modified commercial S-100 cards.
Both systems run using unmodified copies of the TRS-80 Model III ROMS, and come up with the TRS-80 Model III BASIC prompt. They can run TRS-80 BASIC and machine language programs, and the unit with the disk controller boots Model III TRS-DOS exactly as if it were a factory TRS-80.

13 slot backplane, 32K of memory but no disk controller.

Also a 6 slot backplane, 64K of memory, with a homebrew disk controller and dual diskette drives.


I was just a tad too young and with too little money to participate in the S100 era. But the idea of a dozen cards in a proper case (with proper PSU) is rather attractive.


The two machines above are just a small part of Dave Dunfield’s impressive collection of old machines, accumulated over 30 years.

Though I particularly like his early 80’s homemade ‘portable’ 6809 system


And which he wrote all the software for it.

  • The CUBIX operating system
  • All the standard file and system maintenance utilities
  • Several editors, including a fairly decent one which operates line by line or full-screen visual. (The system includes a TTY specification subsystem which allows you to taylor the screen oriented programs to pretty much any terminal.)
  • HELP : A vax/vms like help command, which provides interactive documentation to all commands, applications and utlities.
  • ASM : 6809 assembler
  • RAID : A fairly powerful 6809 debugger.
  • BASIC : A BASIC interpreter
  • C : A complete implementation of my Micro-C compiler (in fact the 6809 was the first target for the compiler).
  • FORTH : A very fast FORTH which compiles to directly executable 6809 machine code instead of threaded lists.
  • MAPL : A little APL system.
  • SIM80 : An 8080 simulator - allowed me to run most of the code I had written for my Altair on CUBIX (I included on the disk as examples, an 8080 BASIC interpreter, and an 8080 CHESS program)
  • Lots more…

It is sad that he is having to sell it all off (due to a serious accident last year).

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Wow, nasty accident and a very lucky escape. What an excellent stack of software though!