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

Paul Koning paulkoning at comcast.net
Tue May 3 13:15:56 CDT 2016

> On May 3, 2016, at 1:55 PM, Erik Baigar <erik at baigar.de> wrote:
> On Tue, 3 May 2016, Paul Koning wrote:
>> No, the PDP-11 offered this starting with the 11/45, in 1971.
> OK, that is a hint - the 11/45 also had a MMU and obviosly must
> have been a great machine for multi-user stuff.

Keep in mind that mapping and protection are not required to build a multi-user system.  DEC did timesharing on the PDP-11/20 (RSTS-11) and on the PDP-8 without either.  And multiprogramming goes back much further, at least as far as the THE operating system in 1964, on the EL-X8.  That OS is particularly interesting because it has virtual memory and demand paging without any hardware help, without address mapping or protection.

In all these cases, you need help from the compilers to keep things safe.  Burroughs mainframes do the same sort of thing, though that's not so obvious: the OS security is dependent on the fact that ordinary users can't write and execute ESPOL programs.


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