To 1P or 4P, That Is the Question

A project log for OSI Challenger 4P Reproduction

I am making a full sized Challenger 4P reproduction, a 6502 based personal computer from the late 1970s.

Michael GardiMichael Gardi 10/31/2022 at 17:270 Comments

Over the course of their six year run from 1975 to 1981, Ohio Scientific sold a wide range of computer products from the low end Model 500 single-board computer to high end Challenger III disk based business systems selling for $13,000 or more (in 1970s dollars).

The lowest cost OSI offering was the  Superboard II, a compact and simple single-board computer. This entry-level system featured a keyboard, video display, audio cassette, BASIC-in-ROM, and up to 8K RAM for around $300. The Challenger 1P was basically a Superboard II with a case and power supply. Both were part of the Ohio Scientific Challenger 1 Series.

In 1977 Ohio Scientific launched a number of systems in their Challenger 2 Series, the smallest of which was the Challenger 4P. Similar to the C-1P but on a standard OSI 48-pin bus, this system is composed of separate boards including a 6502 CPU board, a 540 video card, and a keyboard all mounted in a nice case. With a newer graphics card than older systems, featuring a whopping 2K of video RAM, a 64-by-32 character display was supported.

My original intent was to do a Challenger 1P reproduction, however I am finding that the 32x32 character display (24,24 actual) is a bit limiting. Since a bare bones Challenger 4P system is similar to the 1P but with a 64x32 character display I feel this might be a better choice. To that end I have updated my emulator to support the 4P in addition to the 1P. You can switch back and forth by selecting the appropriate monitor rom at startup (cwmhigh.hex for the 4P or synmon.hex/cegmon.hex for the 1P). 

There is another reason for choosing the Challenger 4P model for reproduction. The cases for both systems are quite similar but not quite identical.

The Challenger 1P on the right has a base and sides made out of a single U shaped piece of metal. IMHO this does not compare to the beautiful wooden sides of the Challenger 4P. I actually have a nice piece of walnut that would work really well. So the case will be built as a 4P with walnut sides, but of course will be selectable for 1P or 4P emulation.

All of the above changes have been posted to this projects GitHub repository.

Updated 12/15/2022:  I have changed the project name and description to reflect the change in direction from a Challenger 1P to a Challenger 4P reproduction.