Adding additional memory to 11/45s

[utzoo!duke!decvax!ucbvax!Mike at BRL]

From:      Mike at BRL
Folks -
	There are two commercial products that I know of which
can be used to add 22-bit addressing (with a PDP-11/44 style Extended UNIBUS)
to older PDP-11 machines (34, 35, 40, 45, 60).  They are:

	1)  The "CAPPER" from Bedford computer in MA.
	2)  The "ENABLE/34" from Able Computer (just announced at Austin USENIX
	    meeting).

There are various advantages to both of these products.  Fortunately,
UNIX mods are availible already for both -- Bedford supports their
product on V7 UNIX, but it requires a lot of kernel mods.
Clem Cole at Tektronix has done the ENABLE/34 UNIX mods, and due to
a superior hardware design, almost no changes are required.

The Able product has the advantage of allowing one to continue
using existing memory, whereas the CAPPER requires all new (11/44 style)
memory.  With the cost of memory today, you may not care.

The CAPPER requires two wires to be added to the backplane for use
with I/D machines (/45, /55), whereas the ABLE one does not need this.


			   CAPPER Diagram

		    (UNIBUS)		  (11/44 UNIBUS)
	Processor ------------- CAPPER ------------------------ Term.
                     |     |              |         |
                     |     |              |         |
                     |     |_ NPR devs    |         |_ Future /44 bus devs
                     |_ Non-NPR devs      |_ 11/44 style 22-bit memory


			   ENABLE/34 Diagram

	Processor ------------- ENABLE ---------- ISOLATOR ----------- Term.
                     |     |                |                 |    |
                     |     |                |                 |    |
                     |     |_ NPR devs      |_ 11/44 style    |    |_ Old mem
                     |_ Non-NPR devs           mem & devs     |_ Non-NPR devs

Personally, because I trust ABLE, because of the simpler usage of the hardware
and greater ease of converting UNIX, and because old memory can be re-used,
my own opinion is that the ABLE board is the better choice.

I had a long chat with the President of Able about the possibility of
using their product to give split I/D on an 11/34 class machine, and the
answer is that, while it can be done, the associated kludges necessary
render this a very distasteful option.  The difficulty revolves around
the fact that the ENABLE board only contains a new set of PAR registers;
the PDR registers remain integrated in the 11/34 processor.  To implement
split I/D properly, an extra set of PDRs is necessary.  The only kludge
to circumvent this would be to have UNIX make all I/D processes max-core
split I/D, so that the PDRs could all be set to "Full size, R/W access".
Other than this problem, there are enough hooks into the hardware to make
it work (just barely).  If you really think this is something you want
to do, I'll be glad to talk to you about it individually.

				Cheers,
				-Mike Muuss