Magic Smoke




This page chronicles the building of a PDP-11/53 that will run 2.11BSD UNIX, and contains hard-to-find information that will help you do the same.

 Here's my first KDJ11 CPU board that I got for $46 on eBay:

This is a KDJ11-DA, M7554-DA. This board has a 15 MHz J11 rev 8 CPU, two serial ports, and a half meg of RAM. The same board is used in the DECserver 500 and 550. The DECserver boards have 18 MHz rev 9 CPUs and either .5 or 1.5 megs of RAM.

The KDJ11 info page documents what you need to know to use this board as a PDP-11/53.

I bought two DECservers on eBay for $10 each. Each came with a 10 slot Qbus, power supply, Ethernet card, and a KDJ11 CPU. There's a lot of iron in a DECserver. Shipping from Columbus to Cleveland via UPS was $40 each. One is a 500, and came with a KDJ11-PB with .5 megs of RAM. This is an older board, using the older layout as seen at the Visual Field Guide. The second is a 550, and came with a very nice KDJ11-SD, with an 18 MHz CPU and 1.5 megs of RAM.

I'm going to build it in a MicroVAX chassis. I took the VAX boards out and carefully stored them, in case I ever want to do something with it. VAX/VMS is too recent history for me. I still shudder when I think of it.

I didn't realize when I bought it how huge the BA23 chassis was. From the picture, you might think it was about the size of a PC-XT, turned on its side. It's a lot bigger than that, and much longer than appears in the picture. But it has room for lots of stuff in it, and keeps it all in one box that might not get banished to the shop.

A DEC RD54/Maxtor XT-2190 came with the MicroVAX. It initially appeared to be bad, but reformatting it several times has made it useable.

Other useful boards that came with this box:

bulletRQDX3 -- hard drive/floppy controller
bulletDELQA -- Ethernet controller


I originally had no manuals or other info to tell me how to hook this board up to a terminal. After following traces to the RS-232 buffers, and some trial and error, I got it to talk to a terminal. The system boots RT-11 and runs perfectly. It is noticeably (i.e. twice) faster than the 11/23.


The DECservers arrived. The racks were much battered by UPS, but repairable; the cards were OK. One is an older DECserver 500. The CPU is a KDJ11-PB. The CPU is rev -07. It has .5 megs of RAM on-board.

The second DECserver is a newer 550. It has a KDJ11-SD, with an 18 MHz  rev -09 CPU and 1.5 megs of RAM. There are also two Ethernet cards and a great pile of CXY08 8-line serial boards. What can I do with 112 serial ports?

All these cards have S-box front panels. Later I'll drill out rivets and install the older card ejectors so they'll fit the older chassis (chassises?) that I have. You might be able to get one of these cards into a non-S chassis if you hold the latch arms in the closed position as you insert the card. Do not try to engage the latches, they must rest against the front edge of the chassis. I was only be able to get the card about half-way into the connector. If you try this, make sure that you do get a good connection. In some systems, cards that are not properly inserted can lose their Magic Smoke.

Both of the new cards booted RT-11 right away, if I typed "171000G" to ODT. The DECserver CPUs have special ROMs in them to bootstrap from their host VAX over Ethernet, and to do terminal server setup and diagnostics.


I finished porting VTserver to the PC. Last night I followed the instructions to bootstrap 2.11BSD UNIX to an 11/53 using VTserver. The target machine was configured as follows:

bulletKDJ11-PB CPU board from the DECserver 500
bulletAndromeda UDC11 MFM disk controller
bulletMaxtor XT-2190 hard drive
bulletDSD StackPac chassis and front panel

The procedure went smoothly by following the instructions in Steve Schultz's 2.11BSD manual, and Warren Toomey's VTserver doc, and UNIX booted right up. I ran into a couple problems shortly after, but as it was late, I quit. Today I posted some questions to classiccmp.


Progress has been slow. Too many other things to do. I've obtained another KDJ11-SD, and three more RQDX3's. There is some sort of 11/53 manual coming in the mail from Switzerland. I'm working on sysgenning 2.9BSD for the 11/23's. I found the MSCP driver for 2.9.


I received the manual. It is for the older artwork, however, by following traces and ohming things out, I was able to use that manual to figure out most of the jumpers. This info is on the KDJ11 page.

I got hold of a PROM burner, and spent a lot of time experimenting with ROMs. I found the 11/53 boot ROM images, and burned them into 27128s for the KDJ11-DA board, and they work well, but I could not get these ROMs to run in any of the boards that came from DECservers. All the DECserver boards came with 27256 ROMs.

Later I found a 1K resistor that tells the board to expect a 27128. Adding this resistor solves the problem, and the KDJ11-SD is now running the boot ROMs.

I discontinued the chronicle, but have continued the project. Conclusion: You can easily make a very nice PDP-11 that will run 2.11BSD using a KDJ11-SD, RQDX3, an RD54 or XT1140, and some sort of box. The things I've had to learn in order to do this are slowly turning into useful web pages elsewhere at this site.


Last modified: December 31, 2009