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

Erik Baigar erik at baigar.de
Tue May 3 10:52:33 CDT 2016

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?


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