The PDP-6 Monitor came out in 1964 and TOPS-10 was its lineal descendant (the result of progressively modifying the codebase to support different PDP-10 models), whereas the first PDP-8 model came out in 1965. OS/8 first appeared in 1971; I haven't been able to determine when its direct ancestor PS/8 was released. I ran some PS/8 programs under OS/8 V1, but I never ran PS/8 itself.