Memory and I/O protection on the 940

Erik Baigar erik at
Thu May 5 03:48:06 CDT 2016

On Wed, 4 May 2016, Mark Kahrs wrote:

> Al mentioned the 940 so I thought I would fill in the details:
> Lichtenberger and Pirtle extended the hardware to include a page map: 14
> bits of VA was divided into 3 bits of page # and 11 bits of offset.  The 8
> pages were held in 2 x 24 bit words divided into a 8 x 6 bit page numbers.
> The high order bit of the mapped page number served as the Read Only bit.
> This meant that "subsystems" (a.k.a. applications) could be shared between
> users.
> Additionally, the instruction set was protected against users with specific
> prohibition against using the I/O instructions.
> This was described in FJCC 1965 with modifications done in 1964.

Yes, perfect match to the criteria in my question! Here we have an other
very early one...

     Thanks, Erik!

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