When did Memory- and IO Protection Emerge (Esp. in Minis)?

Dear Experts, during discussing the Rolms I came accross the following question: What was the first (Minicomputer) architecture which offered memory- and IO protection? I'd define the minimum requirements as: - Existence of a superuser mode (Rolm calls this Executive mode) - Existence of a user mode (With at least two users, Rolm offers 4) - In superuser mode, IO and memory protection for each user can be set up individually. - Any access violation is trapped and handeled by superuser code. - Of course commands for mode switching and setting up the memory and IO ranges must exist. I have got a real machine (Rolm 1602) having this implemented and dating from 1975. A document on this "Access Protection Module" as Rolm calls it also is dated 1975. It consists of a microcode module which realizes an extension of the 16 bit Nova instruction set and an additinoal CPU module, taking care of the new modes and supervising the IO- and memory accesses. My question is not regarding virtual memory memory, but regarding protection (IO and memory) to ensure capsulation of indivitual processes - not necessarily for multi user environments but e.g. for safety critical applications... Probably OS/2 in 1987 was one of the first home computer OSes to support memory protection (how about IO protection?), BSD on some Digital PDP-* was earlier (1977?) but still after the 1602. Any hints out there on other "Mini" architectures of that era having someting similar? Erik.