Qbus split I&D?

Johnny Billquist bqt at update.uu.se
Wed Mar 18 13:07:47 CDT 2015

On 2015-03-18 16:28, Paul Koning wrote:
>> So what happens if one does a reference to something in the range 17 000 000
>> to 17 757 777 on the 11/84? The 11/84 _does_ support having memory on the
>> UNIBUS (up to 248KB), _but_ how it appears depends on how much there is. (See
>> section 3.13.2, EK-1184-TM-PR2.) There's a special register to configure it
>> (the 'KTJ11-B Memory Configuration Register', KMCR), which includes _how
>> much_ UNIBUS memory there is.
>> ...
>> Basically, it seems like DEC was determined not to waste any address space on
>> the J-11/UNIBUS machines. Either it's configured as UNIBUS memory, or it's
>> PMI.
> Interesting.  I was referring to what I learned by reading the RSTS/E memory size determination code.  That code says that the main memory limit is 2M - 128kW for 11/44 and 11/70, and 2M - 4kW for J-11 Unibus.  So it looks like RSTS/E doesn’t support the mixed case you mentioned, only the “just PMI” flavor.

I'm not sure RSTS/E needs to explicitly know if there are Unibus memory, 
except if you end of with non-contiguous memory because of this.


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