PDP-11/45 RSTS/E boot problem

Paul Koning paulkoning at comcast.net
Mon Feb 11 12:29:48 CST 2019

> On Feb 11, 2019, at 1:13 PM, Jerry Weiss <jsw at ieee.org> wrote:
> On 2/11/19 11:50 AM, Paul Koning via cctalk wrote:
>>> ...
>> You may be thinking about PC controllers like the floppy controller.  I can't remember ANY DEC DMA device controller that had boundary crossing limits of any kind.  It certainly isn't a restriction in the RK11.
>> 	paul
> Though not a disk controller, the DEC DR11-B/DA11-B would not cross 64K boundaries.
> I did however via a single chip "dead bug" modification, modify one to accomplish this.      
>     Jerry

That's rather shocking.  I meant my comment to apply to every DMA controller, not just disks.  I never used the DR11-B, though.  Perhaps there are other obscure devices that get this wrong.  But, for example, even devices like DMC-11 and TS-11 got it right.

There are of course Q-bus devices that only do a partial address space, but my point is that whatever the number of address bits implemented, address arithmetic is as a matter of normal design done across all of them, not across a subset.


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