Text File

Aucbvax.2202 fa.unix-wizards utzoo!duke!decvax!ucbvax!Mike@BRL Thu Jul 9 16:44:56 1981 Re: Adding additional memory to 11/45s 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

----------------------------------------------------------------- gopher://quux.org/ conversion by John Goerzen <jgoerzen@complete.org> of http://communication.ucsd.edu/A-News/

This Usenet Oldnews Archive article may be copied and distributed freely, provided:

1. There is no money collected for the text(s) of the articles.

2. The following notice remains appended to each copy:

The Usenet Oldnews Archive: Compilation Copyright (C) 1981, 1996 Bruce Jones, Henry Spencer, David Wiseman.