29 Apr
2020
29 Apr
'20
8:51 a.m.
L.S.
Well, look in Tops10 monitor sources and in the engineering stuff: multiple Unibus
adapters (up to 4, standard 2 provided) each which its own mapping hardware and
registers.
It can easily expanded to even handle 4 MW memory space (I run here some 2 MW variants),
but the current Tops10 single section monitor cannot handle the needed page mapping in
monitor mapping space very well.
1 MW works fine though. 1 MW variants surfaced somewhat later than the 512k ones.
R.V.
-----Original Message-----
From: owner-hecnet at Update.UU.SE [mailto:owner-hecnet at Update.UU.SE] On Behalf Of
Johnny Billquist
Sent: Wednesday, 29 April, 2020 08:14
To: hecnet at Update.UU.SE
Subject: Re: [HECnet] VMS/RSX Guest accounts
I should point out that I actually suspect the 2020 have a Unibus map, just as the big
PDP-11s or any VAXen have.
Which then remaps the Unibus address space to the larger address space of the machine, so
that DMA can go anywhere.
Johnny
On 2020-04-29 08:10, Johnny Billquist wrote:
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:
--
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
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.