I thought this worth passing on. Chris Fenton is an American hacker who's earned substantial kudos for implementing a Cray-I in an FPGA, and doing various other stuff "for fun". Here's what happened when he ported some software to an old CP/M computer:
"The fantastic thing about TP is that not only is it a perfectly reasonable programming language, the software is a full IDE that fits in 26KB! It includes a great text editor as well as a compiler with nice debugging features – seriously, programmers these days could learn a thing or two about writing compact software. Imagine a full IDE that fits comfortably in your CPU’s L1 cache?? That was actually one of the biggest surprises of this experience – the edit-compile-debug loop that anyone writing software is so familiar with is really nice on this machine. It’s probably better than my ‘modern’ programming experience when I’m working on less-retro things. Sure compiling can take a few seconds (probably <15s or so), although this would be mostly alleviated by a RAM Disk, but the 80-column screen is nice and spacious, the mechanical keyboard is nice and clicky, and the mono-tasking nature of working on a computer with 64KB of RAM means no distractions. I had always assumed that writing software on the Kaypro would be extremely unpleasant at best, so this was a nice surprise.
"Getting back to the actual porting process – I started by literally translating the source code from C++ to TurboPascal. It turns out very little re-factoring was necessary to make this happen, although I had to stop frequently to look up the right syntax (some of which feels a bit odd by modern standards). TurboPascal feels like a decently ‘modern’ language, though, and it didn’t take very long to get comfortable with it."
He wasn't happy about the relative performance of a 4MHz Z80 and the microcontroller he'd originally written the code for:
"I actually considered taking this to an extreme and replacing the stock CPU with an FPGA containing a very fast Z80 implementation along with all on-die RAM. I’ve seen people running Z80 cores at ~80 MHz, which would have certainly sped things up, but I decided that this would probably have violated the spirit of the project too much."
http://www.chrisfenton.com/dd9-kaypro-edition/ via
https://hackaday.com/2018/04/08/orbital-mechanics-on-a-vintage-kaypro/