I wrote a 4 pass (scanner, parser, optimizer, code generator) C compiler in 1980 for the 6809. It needed multiple passes because it had to run in 48K.

You beat me to it.

I have a concept of a plan.

My high school didn't have a computer room as I recall, but there was an ASR33 in the math teacher's room that let us program in Basic. I had high hopes of writing a game that recreated the board game "The Fall of Rome" from Strategy and Tactics magazine. That effort was an utter failure, but I did learn how to program in Basic. It was in 1973 or 1974.

A Processor Technology SOL-20. It was a kit with the parts in plastic bags. I put it together and it didn't work. Took it to the Milwaukee Computer Store on North Ave and the tech guy (whose name I forgot unfortunately) told me I could have used a little more solder on the pins but the root cause of the failure was that I didn't properly insert one of the pins on the EPROM monitor. It was bent over. He straightened it and all was good. That was around 1977. I used the Intel 8080 data book to learn how to program it. Later I relocated the monitor to give me enough address space to run UCSD Pascal. Fun times. https://en.wikipedia.org/wiki/...

Most likely this system was running UniFLEX. Uniflex was a small, very Unix-like OS that did feel a lot like Unix, maybe V5 or V6. As I recall the kernel was about 16K and written in assembly language. I only know this because at one point I disassembled it and clearly some parts of it were not generated by a compiler. Not to go into great detail, but one example was a function that looked at the return address to find out where it was called from to act differently depending on the caller.

Many of these systems handled memory above the 6809's 64K address space by feeding the top four address lines into the address lines of a 16x8bit RAM chip creating an address space of 256 4K pages (up to !MB!) that could be mapped into an individual process's address space. It was a cleaver little hack.

I just found this link: https://en.wikipedia.org/wiki/... It's funny because in mentions the Introl C compiler, which I happen to have written.