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Our Retro-Computer Projects

Our Retro-Computer Video Series

EP2 Video Series

Please don't email asking us to sell you a board. We have tried to give Grant Searle some beer money for his hard work. We posted on Grant's Twitter feed with the hope of starting a conversation about this. No response so far. Others report the same from trying to get ahold of Grant. He did post this project publicly with permission for personal use with the only requirement be that he is attributed which we have retained in the source code as he requested. We are not charging for Grant's code in accordance with his licensing.

Video Series

EP4 Video Series

S120 Bus Computer

Back in 1977 (before my Ohio Scientific SuperBoard II I had my own homebrew computer. I never took any pictures of it and the hardware is long gone now. These are the pieces of it I remember.

  • Ran on Elco? 120 pin edge connector cards
  • 6800 Processor board running at 1 MHz
  • 2K of Static RAM board
  • 2716 EEPROM board (may have had 4 sockets total, don't recall for sure)
  • Front panel switches and LEDs to enter the address/data (Step/Insert) and blink lights

I remember getting it to run and I do remember blinking a light back and forth on it. Once I got the SuperBoard II, I stopped working on my own board.

It might be fun to reproduce that board!

Pieces to Reproduce my original S120 Bus Computer



Ohio Scientific SuperBoard II - My first commercial personal computer


SuperBoard II

  • Manufacturer: Ohio Scientific
  • Model: Superboard II ( Model 600 )
  • Available: 1978
  • Price: US $279 assembled
  • CPU: 6502
  • RAM: 4K static RAM, 8K max
  • CEGMON - Monitor in 4K of EPROM
  • Display: composite video, 30 X 30 text
  • Built-in keyboard
  • Single board design
    • I eventually got a RAM expansion card with Floppy Disk Controller
  • Ports: composite video, cassette
  • Storage: cassette
  • Microsoft BASIC
  • 2K Monitor ROM (CEGMON)
  • Compkit 101 - British clone of the SuperBoard II

Superboard II Documents

CC65 - C Compiler for the 6502 and OSI C1P

SuperBoard II Emulator

BASIC Programs

10 I=1
30 I=I+1
40 IF I < 5 GOTO 20

SuperBoard II/ Retro-Tech Refresh

I was looking around for a way to recreate my OSI Superboard and found Grant Searle's design.

  • Compukit 101 video

6502 Computer Projects

Grant Searle's FPGA MultiComputer Project(s)

Retro-Computer Map EP2 to EP4 card

My Build of the Z80 Version


Retrobrew Computer Builds of the Multicomp Project(s)

Neil Crook Builds of the Multicomp Project - 6809 Version

Neil started from Grant Searle's work and fixed a number of issue with the VHDL code.

CP/M Resources on the Net

CP/M Notes

  • CP/M is not case sensitive
  • REN NEWNAME.EXT=OLDNAME.EXT - Rename a file from the old to the new name
  • ERA FILE2ERA.EXT - Erase a file
  • Asterisk is wildcard
  • .COM are command files
  • PIP - copy command
  • Drive references A:
    • Drives go from A-???
  • LS is a better direction program

Microsoft BASIC Notes

  • SYSTEM -- Return to CP/M
  • NEW - Delete program
  • OUT 132,1 -- Output to I/O port 132
  • PRINT MEM - Free memory (6809 Extended BASIC)


Grant noted about the SD card interface:

... the SD controller is easy to control - in BASIC POKE the sector number, POKE the write command, 
POKE 512 bytes to the same location to write a sector, 
or POKE the sector number, POKE the read command, and PEEK 512 bytes to read a sector.

DEC (Digital Equipment Corp) Computers

18-Bit Family Timeline
1960 PDP-1, Digital Equipment Corporation's first 18-bit computer
1963 PDP-4
1964 PDP-7, uses flip chip modules; used by Ritchie and Thompson to develop UNIX
1966 PDP-9, program compatible with PDP-7

1969 PDP-15 replaces PDP-9
1972 MUMPS-15 (Massachusetts General Hospital
         Utility Microprogramming System), PDP-15 -based timesharing system designed 
         to handle medical records, still in use
1979 PDP-1 with working Spacewar! game installed at
         The Computer Museum, Boston
1988 A PDP-1 system (serial no. 44) is saved from a barn in Wichita, Kansas, 
         and donated to the Digital Historical Collection


There are three known PDP-1 computers in existence. Fifty were originally produced.



External Sites

Grant Searle Terminal Design



RetroBrew Computers Sites