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Ohio Scientific Challenger C4P

Manufacturer Ohio Scientific
Model C4P
Date Announced 1979
Date Canceled 1981 (with sale of company)
Number Produced Tens of thousands
Country of Origin USA
Price $1,700 (system with floppy drive)
Current Value $300+
Processor MOS 6502
Speed 2 MHz
RAM 8K-48K
ROM 8K BASIC and Bootstrap/monitor
Storage Cassette or 5.25" floppy"
Expansion External devices
Bus N/A
Video Composite video out, 16 color, 32 lines x 64 characters
I/O Cassette IO, Parallel, Serial,
OS Options Proprietary OSI OS 65D
Notes The OSI Challenger line used a faster version of the MOS 6502 than its competition. This extra speed didn't help the OSI in the market, however, and the company eventually faltered to stiff competition from Apple and Commodore.
Related Items in Collection Manuals, some disks.
Related Items Wanted Additional software.

The OSI C4P in my collection is the MF model (for Micro-Floppy) that came with 24K or RAM and the floppy drive.

OSI C4P monitor prompt

This system is partially functional and boots to the "monitor" prompt of H/D/M. D should start the disk drive and M should enter the monitor but neither works at the moment. I suspect a RAM error but will have to dig deeper to be sure.

OSI C4P Manuals
OSI C4P Manuals
OSI C4P Manuals
OSI C4P Manuals

This system came with a couple of binders full of documentation and software.

OSI C4P Tutorial Disks

Included was the C4P tutorial. Unfortunately disk 2 is missing.

OSI C4P disks

Along with the boot disks there are a bunch of Aardvark software disks.

OSI C4P Rear View

The rear of the unit shows a bunch of ports and connections.

OSI C4P Drive Interior

The inside of the disk drive shows it to be a fairly straightforward unit.

OSI C4P Internals

The system, on the other hand, is far more involved with several boards stacked into the small space.

(Submitted March 25, 2011 11:20:32 by (a href=mailto:peter.arntatgmaildotcom)Pete Arnt(/a))

I worked for an OSI reseller in Sarasota, FL back in 1980-81. Mostly large C3B and C3C systems running OS-65U, OS-DMS and custom software. Wondering if anyone out there has access to a readable copy of OS-65U? Given that and a set of schematics for the hardware, it would be fun to write an emulator for these systems.

(Submitted September 24, 2010 14:53:42 by John Carpenter)

I was lead technical writer for OSI after M/A-COM bought the company from Mike and Charity Cheeky, and moved engineering and marketing to Bedford, MA in 19882-83. M/A-COM tried to transform the OSI product line from hobbyist into small business computers. I worked mainly on the MasterKey product line, which had three CPUs and ran most apps with CP/M on the Z-80 chip. We got killed by IBM's roll-out of its PC. The market changed in a week. I can answer some Ohio Scientific questions (from dim memory), and I still have a couple manuals in a box in the garage.

(Submitted February 24, 2010 19:10:35 by Dave Pompea)

I see one of the Aardvark disks is Galaxia. I'm the guy that wrote that program, back in the early 80's.

(Submitted January 26, 2010 23:29:04 by Bob)

CPU should be 6502A.

(Submitted December 7, 2009 23:46:34 by tom paulson)

i would like to buy a C1P, if you ever run across a working one

(Submitted September 17, 2009 12:40:46 by Peter Sanders)

I think I have some of the drive pads that used to be placed on the other side of the disk drive head to help with reading the disk data. If I do still have them do you want them along with an old OSI 5v power supply?

Kind regards


(Submitted June 10, 2009 17:16:33 by xsoliman)

In the UK, the the OSI Superboard was 'copied'? and sold as the Compukit UK101. It was my first computer. Didnt have a disk drive

(Submitted November 4, 2008 13:45:11 by Mike Pennock)

I have a one of the OSI that was a later model. It has 32k memory with a 1/2 hight disk drive attached. When OSI was going out of business, I obtain the protype board on the system that was for the color monitor. I have all of the manuals and disk for the system.

(Submitted March 28, 2008 15:37:36 by Steve Gray)

I noticed your OSI C4P doesn't boot... first thing to check is that the CAPS LOCK key is down as the H/D/M? prompt is looking for a capital D! ex.html


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