Memory and I/O protection on the 940

Erik Baigar erik at baigar.de
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!


More information about the cctech mailing list