[Info-vax] RB730 Integrated Disk Controller (R80/RL02) usable with VAX-11/750?

[Johnny Billquist]

On 2011-05-05 07:02, Bob Koehler wrote:
> In article<ipt5am$d6v$3 at Iltempo.Update.UU.SE>, Johnny Billquist<bqt at softjar.se>  writes:
>>
>> That's what the Unibus Map is there for. The Unibus map sits between the
>> Unibus and the memory, and remaps DMA from the Unibus into the larger
>> address space of the memory bus. Same both on the 22-bit capable PDP-11s
>> and all VAXen. The exact details of the Unibus map differs between a
>> PDP-11 and a VAX, though, but the principles are exactly the same.
>
>     Too me, that map is part of the memory subsystem.

By the way, an important point contradicting this view. When the CPU 
access memory, the Unibus map is not involved. If the Unibus map was 
part of the memory subsystem, the CPU would have no way of avoiding it, 
so it don't really make sense to look at the UBA as a part of the memory 
subsystem. (On a PDP-11/70, when massbus do DMA, the Unibus map is also 
not involved, it is only involved in DMA from the Unibus. The same is 
true for all VAXen.)

	Johnny

-- 
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