I wrote a bios to try to get CP/M up and running on my IMSAI. It does require a lot of deep knowledge about the machine which admittedly was more common in tho

I wrote a bios to try to get CP/M up and running on my IMSAI. It does require a lot of deep knowledge about the machine which admittedly was more common in those days. However I suspect most people bought a pre-packaged system. If you were doing most of your coding in BASIC its unlikely you'd be able to modify the BIOS.