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OHIO Scientific

Little information about this C2 system composed of a computer case and a separate floppy drives case.

The system pictured is a C2-OEM-4. [OEM] means it could be bought by other computer companies that could put their own brand label on the case. [4] means dual case version.

The main system was based on an 8 slot backplane (ref. 580), a 6502 processor board, along with a floppy disc controller and a serial port for the video terminal (ref. 505), and 3 x 16 KB static RAM boards (ref. 520). Ohio Scientific and various third companies provided several additional Memory and I/O boards for this system.

The floppy case had two Siemens single sided 8" 275 KB drives. With single sided drives user could copy to both sides of the floppy by removing the disk, turning it over and use the back side.

OSI delivered a specific operating system called OS-65U along with Business BASIC, a powerful BASIC interpreter, and various demonstration programs.


Thanks to Dan Schwartz for this additional information:
There were a variety of C2-series computers: The C2-4P and C2-4P MF (mini-floppy), the C2-8P and C2-8P DF (dual floppy), and the C2-OEM, which usually came in a single, longer case containing both 8" floppy disks and the CPU and backplane.
The C2-4P was renamed C4P when they added wooden sides to the case. The computer shown looks like the C2-8P DF, but the stated C2-OEM-4 designation could easily be correct. C2-OEM computers were set up to use a serial terminal, rather than an internal video board (producing a rough approximation of NTSC video) and "polled"(software-scanned) keyboard.

OSI was said to be the first company to offer microcomputers with hard drives, starting in 1977. Those drives were huge 14" monsters that took two men to lift!
OSI's two operating systems - OS-65D and OS-65U - both used heavily modified versions of what was originally the same version of Microsoft BASIC. In 65U, the business OS, there was no clear separation between the BASIC and the OS kernel; in 65D, the home-oriented system, there was.
OSI's floppy disk system was unique in that it used a serial port (ACIA) chip to read and write data to the disk. Every byte of data on the floppy actually had a start bit, a stop bit, and (under 65D) a parity bit. 65U programmed the hardware differently than 65D, so the two operating systems could not read each others' diskettes, although 65U included a limited utility to read raw sectors from 65D diskettes.

While I no longer have my OSI computers, I do still have a 12" black-and-white TV that was modified by OSI to work as a monitor, by adding A/V inputs, which normal TVs of the era did not have.

We need more info about this computer ! If you designed, used, or have more info about this system, please send us pictures or anything you might find useful.
Please consider donating your old computer / videogame system to or one of our partners from anywhere in the world (Europe, America, Asia, etc.).


I have a lot of info on OSI as I was selling them back in 1979-1980. I even still have a Challenger C3 without hard drive and a 19" rack supplied by OSI. I would be happy to help with anyone looking for details of the time.

I now regret dumping my Okidata 22 line printer, only two years ago. It still worked but had trouble with PC parallel port interface. The trouble was that the standard PC was sending something that woudl do a page eject about every two lines. This is an era before the laser printer. The paper was wide 15"(i think) tractor feed fanfold computer paper. A page eject on the Oki22 was very fast, about two seconds. (I was never able to find a PC driver for the printer.)

Friday 15th August 2014
Ed Miska (USA)

I still have a C2-OEM. I have a Televideo terminal and a NEC Spinwriter printer for it. The C2-OEM I have is in a single case with dual 8" floppies. I have added memory and a printer card. I still have the OS 65D Tutorial and OS manual, and I may even have the full schematics. Have not started it up for years. In 2000, I took it to a vintage computer fair and ran Adventure on it. I would have to take it out of the attic to do an inventory of the cards.

Wednesday 12th September 2012
Simon Favre (USA)

This was my first serious computer (I started with TRS-80) which I bought in Boston in 1980 or 1981 (I think). I did a lot of work with this guy and even earned a living with it here on the downeast coast of Maine for several years.

It is a C2-OEM with 1 6502 cpu, 2 8" disk drives, and a serial port for a terminal (Hazeltine model ??, long gone) and a long parallel cable for my old Centronics tractor feed(also long gone).

Friday 18th December 2009
Jim Cummins (USA)


TYPE  Professional Computer
YEAR  Unknown
KEYBOARD  Depending on the video terminal used
CPU  6502
RAM  48 KB (Depends on the configuration)
ROM  Unknown
TEXT MODES  80 chars x 25 lines (Standard video terminal)
SOUND  No sound
I/O PORTS  Serial
BUILT IN MEDIA  2 x 8'' 275 KB floppy drives
OS  OS-65U
POWER SUPPLY  Built-in power supply unit
PERIPHERALS  Various OSI cards
PRICE  Unknown

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