KM11s and the PDP-11/20 (was Re: Help w/DEC H742 +15V...)

Date: Tue, 14 Apr 2009 00:55:18 -0400 Subject: KM11s and the PDP-11/20 (was Re: Help w/DEC H742 +15V...) From: ethan.dicks at gmail.com To: cctalk at classiccmp.org On Mon, Apr 13, 2009 at 10:13 PM, Josh Dersch wrote: No. I wish I did, but I got a pair of KM-11s since I have several DEC devices which can use them (RX01, RK11-C, RK11-D, PDP-11/05, PDP-11/20). I don't happen to have an 11/40. The primary purpose for my KM11s, was to facilitate the restoration of my 11/20 - it was butchered and dumped prior to me acquiring it (I rescued it from the skip at work, already in many pieces), and to attempt to get my RK11-C working (it arrived from the same place intact, but is suffering from some visible corrosion on the pins of the backplane, so I don't know if I'll ever get it working reliably). I don't need to do much RX01 electronic repair (a new drive motor and a new stepper motor would go a long way to returning both sides of a dual drive to work, but the boards seem intact); however, I think it'd be cool to watch the drive work by observing the blinkenlights. These items are way, way down on my DEC list (I have PDP-8s to work on first), but someday the 11/20 will bubble up to the surface. I know I don't have all the core that originally came with it - one of my cow-orkers souvenired it 20 years ago. I have the backplanes and the driver boards, but am missing at least one 4K core plane. My _hope_ for this system is to get an older version of RT-11 up on it first, then *perhaps* if I can get enough memory on it and some compatible disk device, see if there's an ancient-enough version of UNIX in the PUPS archive to run on it (it would have to be a version from 1971 or 1972, IIRC, to fit on a KA-11 w/16-bit address bus). I don't know that it's possible, but it's a goal. First, though, I have a lot of reconstruction to do on the 11/20. IIRC, I will need some PSUs to get the ball rolling, since that's what I think was yanked from it before it was trashed. I think I have the CPU box plus two memory boxes (the size of 3 BA-11s, essentially), but I don't recall the PSU model number off the top of my head - it's one that supports multiple single-height power cards in a series of DD-11C-sized 4-slot hex-height backplanes. Oh... I probably don't have enough M920s to reconnect everything - I don't think many of them were in the dumpster with the CPU. *Sigh* The missing parts is why I never did much with it. Maybe I'm better off trying to recycle the front panel and drive it from something modern. The chances of finding multiple PSUs and short Unibus interconnects that aren't already in an 11/20 seem small these days. -ethan