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[Johnny Billquist]

Nope. Unibus can only address 128Kword, and in this context that is 128K 
of 18-bit words. So you cannot even DMA into a full 256K of 36 bit words.

   Johnny

On 2020-04-29 05:51, Thomas DeBellis wrote:
> You know, I have been racking my brains from time to time and I can't 
> remember a thing about the ADP modifications to the 2020.
> 
> So, the 2020 came with a maximum of 512K words, 2**9.  An addition bit 
> would have brought it up to a full megaword, 2**10, which is quite 
> reasonable for the target audience (some kind of installation that 
> didn't hold stock in the local power utility).
> 
> I guess there may have been modifications to the 2020 build of the 
> monitor to allow for the extra bit.  I don't know if the Unibus devices 
> could do DMA into the full address space.
> 
> Did you pick up any software with these little jewels?  The monitor 
> changes might be interesting.
> 
>> ------------------------------------------------------------------------
>> On 4/24/20 12:12 AM, Dave McGuire wrote:
>>    Nice!
>>
>>    One of our 2020s is in the brown color scheme.  You know what that
>> means: ADP, and one more address bit.
>>> ------------------------------------------------------------------------
>>> On 4/23/20 6:15 PM, Thomas DeBellis wrote:
>>>
>>> The solution for 4.1 was one of the finest hacks I have ever heard of;
>>> while the 2020 doesn't support extended addressing, it does support
>>> multiple address spaces, so what they did was move all the symbols into
>>> a separate address space.  This was called 'hiding' symbols and I
>>> thought it was great because it made them harder to smash.  However, all
>>> of that went out the window with 5.0, which fully supported extended
>>> addressing.

-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol