[vincent-manis]

And on the issue of using the INT instruction, dispatching into a table of kernel routines is very much not new, going back far beyond the EMT instruction to the System/360 SVC instruction.

Given that Paterson has stoutly denied ever looking at any CP/M code (and nobody has ever produced any contradicting evidence), it's clear that in his “quick and dirty operating system”, he took the CP/M user documentation and built something with somewhat the same architecture and user-visible behaviour, using his own code, and tailoring it to the somewhat more powerful 8086. OS designers have been doing this for decades: look at the documentation for Univac and RCA lookalikes for System/360 (available on bitsavers), and compare to DOS/360. Or that “hobby” system written by some guy named Torvalds...