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

Erik Baigar erik at
Thu May 5 03:46:07 CDT 2016

On Thu, 5 May 2016, Dave Wade wrote:

> I thought we were talking Mini Computers. The Ferranti/Manchester Atlas had
> virtual memory of a sort which provided protection, and indeed IBM bought
> the Virtual Memory patents from Manchester University. I gather the PDP/11
> received Memory Mapping boards early in its life, didn't these offer some
> protection?

Yes, originally I had Minis in mind, and yes - this term is not well
defined. Anyhow I learned a lot from all the answers as many differnet
machines have been covered in contrast to the normally DEC biased
traffic here. What still is a quite interesting question for me is,
that purely "mapped memory" or "virtual memory" does not match the
answerr to my question as it still lacks the IO aspect and I'd call
it only memory protection if there is a method to prevent ordinary
programs from modifying the memory map.

So from my point of view the HP2100 matches the criteria of my initial 
question, the Rolm APM does but probabaly some others mentioned for their 
virtual memory do not. E.g. the DG mapped memory (Nova3 or Eclipse)
lacks the "user prohibited to modify map" feature I think.

And for sure: Atlas was a very interesting machine with great capa-
bilities for its days!


>> -----Original Message-----
>> From: cctalk [mailto:cctalk-bounces at] On Behalf Of Curious
>> Marc
>> Sent: 05 May 2016 01:07
>> To: General Discussion: On-Topic and Off-Topic Posts
> <cctalk at>
>> Subject: Re: AW: When did Memory- and IO Protection Emerge (Esp. in
> Minis)?
>> In the not mini but very maxi category, I just learned that IBM
> implemented
>> memory protection as an RPQ (customer feature) at the request of the MIT
>> folks that built the first IBM time sharing system (CTSS, the predecessor
> of
>> Multics), on their IBM 7094. Around 1963, unless it was already
> implemented
>> in the IBM 7090 which would have been 1961. At least that's my cursory
>> understanding of it from . I was very
>> surprised it was that early!
>> Marc
>> Sent from my iPad
>>> On May 4, 2016, at 3:02 PM, Chuck Guzis <cclist at> wrote:
>>> Is the CDC 1700 considered to be in the family of "minicomputers"?
>>> (i.e. was the word invented before then?).
>>> If so, the 1700 had a rather elaborate system of memory and peripheral
>>> protection.  Circa 1965 (at least that's the date on my manual).
>>> --Chuck

More information about the cctalk mailing list