Brand New (to me) PDP-11/34A ... family

I picked up four new PDP-11/34A machines this weekend, and put together a cabinet with one of them. It needs some real cleanup and I haven’t vetted the PSU so the backplane is unpopulated, but it’s on its way!

There’s a lot of other equipment in this haul, but I haven’t had time to triage anything. In particular, I got some Tektronix 4010/4012 graphics terminals that I’m excited to bring online. There’s also a ton of software for the PDP-11s (all for RT-11 as far as I can tell) on RL01 and RL02 disk packs, as well as a handful of 8" floppies.

It was a 12 hour round trip drive to pick this stuff up, plus about three hours of loading the truck on the other end. It was another four or five hours of unloading, sorting, and storing on this end. The equipment completely filled the floor of a 16x8’ box truck, plus some stacking of the smaller and lighter stuff.

I’m very excited to bring this stuff online, and I’ll keep everyone updated as I make progress. It will probably be a month or two before there’s any real movement, unfortunately. I’d be happy to hear any PDP-11 revival tips people have in the meantime!


What an excellent adventure! Are those Tektronix 4010 storage tube vector displays?
(Edit: oh yes, I see you’ve already said as much!)

Found a few of these in the box of documentation!


My dear companion in the 80ties :wink:

What a haul! Have fun, and please keep us appraised of your progress.

1 Like

Manuals used to really keep it real!



Those Tek terminals @EdS asked about:


A UNIBUS backplane extender:

This one looks like it might have some special routing, but normally it would have two UNIBUS slots (on each side) and two Modified UNIBUS slots (down the center) with four SPC (Small Peripheral Controller) slots below those.

Here’s s closer look at some of the routing and wire wrapping:


Is it really retrocomputing if you don’t have this going on?

It’s been a while, but today a friend stopped by and we started debugging the first CPU. We got the PSU checked out, the KY11-LB front panel console controller installed and working, and the DL11-W serial controller communicating (thus the above abomination). Next is CPU and memory!


Extra points for this combo meeting a real need, and not being one of those spoof concatenations!


It was the easiest way to get from Point A to Point B! The PDP-11 has a DB-25 male on the end of its serial card cable (40-pin-ish IDC on the controller end), the laptop hooked to it has a DE-9 male on its USB adapter. The null modem in between is gender-preserving, so there’s a null modem and a female-to-female gender adapter.

It would have been one fewer adapter had I been able to get the VT105 working, but while we were debugging (of COURSE there was a “null modem” adapter in the mix that was NOT null modem, but pin-to-pin!), since it’s also 25 pin, but at some point it during debugging it developed a RAM or bus problem that caused it to print some gibberish on the screen. I am assuming I need to reseat some boards or chips, but one thing at a time.


I had to build my own cable to make my TI Silent 700 teletype work with my Altair-duino.


It boots! This video is terrible, but it’s what I took in the excitement of the moment:

That’s a shot of the VT100, then me pressing Control+Boot to boot to the onboard monitor from a halted state, and then the monitor prompt on the VT100! I was also able to key in a simple machine program to write a BEL to the terminal at the operator’s console, and it worked.

I attempted to hook up and boot an RX02 drive with a floppy labeled “RT-11 BOOT” and then some faded handwriting I can’t make out, but I couldn’t get it to boot from either drive. It appears that the left drive isn’t spinning, and the right drive (while spinning) didn’t boot with a DX1 or DY1 command at the console monitor prompt. More experimentation is warranted; I have quite a few other RX01/RX02 drive units, as well as drive controller cards. Perhaps one or both is dysfunctional.

1 Like

Yet another progress shot:

This is RT-11SJ, booted from an 8" floppy in an RX02 drive!

It’s been a bit of a journey, and I still haven’t been able to run any diagnostics (which I would dearly love to do), but clearly something is working! I’ve keyed in dozens of programs on the front panel (hand-assembled on paper or in my head, or taken from documentation, or from diagnostic information on the 'net), and I can’t find any problems – but I haven’t been able to boot a tape image from an emulated tape drive. The fact that I can boot the floppy perplexes me! I’ll fill in some of the steps of the journey more, later, but for now I’m basking in brief feelings of success. :wink:


So we’re going to bring back command-line Compuserve, right?

1 Like

Ah - we did find some diagnostics when bringing up the (emulated) PDP-11 second processor for the BBC Micro. They might perhaps be too low-level, but:

Or maybe not too lowlevel, but far too large to toggle in…!

1 Like


The CPU cabinet in the left is actually empty right now, except for a power supply and 22 UNIBUS backplane slots. The RX02 floppy drive in the left cabinet and both hard drives are hooked to the CPU cabinet on the right, as is the VT105 terminal.

I’m currently in the process of backing up my 10MB RL02 disk packs over 9600 baud serial, which takes several hours per disk.


Disks are backed up, I’m running RSX-11M with two local terminals (VT100 and DECwriter IV) and a serial port on a laptop providing a reason terminal for a few friends. The learning continues…


It’s been a while, but I’ve been working on bringing up the second unit. It has presented me with some more challenges than the first (which basically Just Worked), but it’s coming along. Here are some quick photos for those who may be interested!

The cabinet in this unit has three backplanes. PDP-11/34A machines have a special 9-slot backplane for the CPU that has two CPU slots at the far right-hand side. The remaining seven slots are six modified Unibus (MUD) slots and one Unibus slot, each with a small peripheral controller slot (SPC) alongside. This unit also has a 9-slot and a 4-slot backplane installed.

Here you can see the two boards that make up the CPU in their slots on the far right, with (proceeding to the left) a bus terminator/bootstrap card, a memory card, a Unibus jumper and serial line card (with the Unibus jumper jumping over to the next 9-slot backplane), an RL-11 hard disk controller, an RX01 floppy disk controller, and then finally a bus terminator and quad serial line card. The final four-slot backplane visible on the far left is not electrically connected.

The grant continuity cards that are required for interrupts and DMA are barely visible between the large cards, but more visible in this shot:

There’s a reason they call them “knuckle busters”.

The 11/34 is still a wire-wrapped backplane, and the underside is a work of art. The difference between the three different types of backplane in the unit becomes obvious when one looks at the wiring.

The rightmost backplane in this photo is the CPU board, and the middle and leftmost backplanes are Unibus backplanes (Standard Unibus slots on each end, MUD slots in between, and SPC slots alongside every Unibus or MUD slot). In this photo, the Unibus end is at the bottom, and the SPC are above.

There are a variety of interesting features in the wiring that I’ll post about some time later. For now, note the obvious difference between the CPU slots at the far right and the rest of the slots.