HP should open OS/8 and RT-11, the two big influences on CP/M. OS/8 is kind of remarkable, running on a system arguably less powerful than the first 8-bit home computers (I would say they are closer to PIC microcontrollers, but with more RAM):
PDP-8 memory is heavily paged. There are 128 word pages- direct addresses can only reach within the current page, and literals (immediate data including addresses to other pages) have to be allocated out of this current page along with the instructions. Second, there are 4K-word fields. So you need to use far jumps and returns to access outside the current field. This is just like PIC microcontroller pages.
OS/8 reserved only two pages for itself. Things like the command interpreter were swapped out to disk or DECTape.
If the application needed device drivers, it got to choose which pages the drivers would occupy- meaning the device drivers had to be written as position independent code. Also I think each driver was limited to two pages..
https://www.pdp8online.com/os/os8/index.shtml
PDP-8 memory is heavily paged. There are 128 word pages- direct addresses can only reach within the current page, and literals (immediate data including addresses to other pages) have to be allocated out of this current page along with the instructions. Second, there are 4K-word fields. So you need to use far jumps and returns to access outside the current field. This is just like PIC microcontroller pages.
OS/8 reserved only two pages for itself. Things like the command interpreter were swapped out to disk or DECTape.
https://en.wikipedia.org/wiki/DECtape
If the application needed device drivers, it got to choose which pages the drivers would occupy- meaning the device drivers had to be written as position independent code. Also I think each driver was limited to two pages..