The PDP-11/23 Project

(or a Fool and his money are soon parted!)

Almost thirty years ago I bought a PDP-8 with the idea of using it. at the time I did not know how to write in assembler, or basic or much of anything else but did have big ideas. I ended up swapping it for a S-100 system with a Basic interpreter and after that progressing to PC/DOS system and forgetting all about the eight. Now I have reached that point in life where you want to start trying to do the projects that you once started but never finished. with PDP-8 systems selling for stupid money I though that I would try a PDP-11 The Unibus systems with the lights and switches are still quite pricy so I again reduced my standards and went the direction of a Qbus system. so all of this leads me to my PDP-11/23

The Back of the rack with a view of the processor and expansion chassis, the RX02 dual floppy drive and the RL01 removable hard drives.

The Cards in my system are a 8186 KDF11-A CPU, a four port serial controller, a 8029 RX02 controller card, RLV11 RL-01 controller cards, 9400 jumper card to a second 9400 in the expansion chassis, two 8044 MSV11 32K memory cards and last but not least a BDV11 bootstrap / diagnostics board.


The RL01 was built from two non working units. I did buy a new disk pack with a operating system for it and spent a lot of time getting everything running. They are complicated and about as difficult as working on a old analog video tape machine, very similar servo system and head selection system but they are repairable unlike the modern drives of today.

I have been using the worlds oldest logic analyzer and slowly getting one stage to work at a time.


Another item on the list will be getting the Decwrite printer up and running.


Its June  now and the last months have been a non stop DEC funfest! I did purchase the worlds oldest logic analyzer but it has all the cables, adapters and wires with it and in the world of obsolete logic analyzers that's a rare thing. after much time , wire tracing and fabrication I now have the drive to the point where it spins up and reports ready but still having issues with getting it to read. due to lack of progress and other projects around the shop it may be time to put this aside for a while.

As of March of 2010, I have the processor up and running. I can read and write to the memory and execute simple programs using the ODT diagnostics. I have been using this system with a Dec 510 terminal but now know I have to find a older terminal to go with it. When I started working had a PC running terminal software but there's something not right with using a system many times more powerful just as a I/O device for this!

After more online help it was determined that maybe the problem is in the memory, I did find that two of the four memory cards had problems and after removing them from the system and a little work on shuffling around the position of the cards I can now load RT-11 from the RL or RX drive, so now I have a working operating system. still need couple parts to get both of my RX-02 drives running, epically a new belt for drive two, but the big project now will be finding Basic to run on the system. all this happened in February of 2011

Many Thanks to all the people who have helped with this project, using the internet today we can get copies of almost all the documentation for these old systems and I have found that many of the people who have them have always been willing to help with invaluable information.


Additional web links for the PDP-11

Vintage Computer Forum Source of the final solution

                                    Henk's DIGITAL computer room Examples of almost every member of the 11 family

                                    PDP-11 Home Page at Tons of resources

YouTube - Dec PDP-11/23 YouTube video of the system

YouTube - PDP-11 And The RL-01 YouTube video of the RL drive

YouTube - PDP-11/23 2011 Latest video

Rays Web Page

March 2011