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

Paul Koning paulkoning at comcast.net
Tue May 3 11:17:09 CDT 2016

> On May 3, 2016, at 11:52 AM, Erik Baigar <erik at baigar.de> wrote:
> 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.
> ...
> 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.

No, the PDP-11 offered this starting with the 11/45, in 1971.

In larger computers the feature is much older.  Consider the CDC 6600 (1964).  While not all the properties you mentioned apply because I/O is in separate peripheral processors, the notion of a privileged mode and address mapping is there.  And even that isn't the oldest example, I think.


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