Problems with my PDP 11/24 (was:Question about memory boards used n VAX 11/7xx)

From: Ethan Dicks <ethan.dicks_at_gmail.com>
Date: Thu Dec 30 03:41:21 2004

On Wed, 29 Dec 2004 16:05:57 +0100 (CET), Johnny Billquist
<bqt_at_update.uu.se> wrote:
> Actually, the memory system in a VAX-11/750 are specific to that model.
> It's not compatible with the VAX-11/780, nor the 11/730.

Are you sure about that? I recall using the same 1MB boards in an
11/750 and and 11/730. If you tell me I'm mistaken, then I probably
am, but that's what I remember.
 
> However, the memory backplane is compatible with the MK11 memory box for
> the PDP-11/70. Unfortunately, the MK11 controller only deals with 256Kb
> memory boards. So if you'd like to use these 1 Mb memory boards in an
> 11/70, you need a small hardware hack, and a small software hack.

Hmm... I _didn't_ know that (the trick... I did suspect that the 256K
boards were intercompatible).

> The hardware hack is to tie four board select lines from the backplane
> into to address lines for the memory card, and the software hack is to
> reset all the ECC bits in the high 768K of each card, since the MK11
> controller only clears ECC on the low 256K.

Hmm... that's an interesting hack... I wonder if anyone has ever
tweaked 2BSD for that.
As I _have_ two full-boat (4MB) 11/70s, it would only matter if I
wanted to chew up less power by running 4 boards (especially 4
3rd-party boards w/256kbit chips) rather than 16 boards w/4116 16kbit
chips. OTOH, I'd have to _find_ 4 1MB boards beyond the ones I
already have.

-ethan
Received on Thu Dec 30 2004 - 03:41:21 GMT