Hello,
...A long time since I have seen my OSI C4P and C1P computers.
I bought a C1P way back in high-school - so it was pre- 1981. I remember wiring up a cassette player because the audio connections were causing too much problems.
Bought a C4P sometime after and thought it was the world to have color. Later installed a floppy drive controller - also modified the CPU board to replace the BASIC-ROMs with RAM so that I could have more - which I think totalled to 48K?? I wrote a game that was similar to Pac-Man - did it all in assembler, well, it was actually machine code, entering all the hex values directly into memory. Also wrote a very cryptic flight sim - the only visuals were location, speed and altitude - never did much more with it. I do remember loading programs required specifying disk tracks, and memory locations.
I'll need to go look at the web-based emulator Jeff Par created.