Actually, I own two 11/73s. One comes in a really large configuration, the other one is housed in a small DEC BA23 chassis.


PDP 11/73 #1:

Date of production: somewhere in the mid-eighties

CPU type: KDJ11-A,

System bus: Q-Bus

Installed/max. memory: 4096KB/4096KB DRAM

Installed operating system: RSX11-M

Serial number:






Saving and collecting larger systems in fact began with this very PDP 11/73. This system came via ebay and I really didn't know what was waiting for me since the seller didn't upload any photos. Well, it was quite a surprise when we went down the cave of the building in which the PDP was installed in order to inspect what I finaly got. My first thoughts were: "Damn, I'll have to come back in order to take the rest." ... and we came with a big car already! Qbus-based PDP-11 systems not often came in configurations needing more than one cabinet. In addition to the two cabinets, two dozen of RL02 disk packs and many boxes of 8" floppies and reel tapes were available. When I picked up this system, I only had very little knowledge about DEC PDP mini-computers which changed with that 11/73.

This system worked in a small engineering company for almost 20 years! It was used in the year 1999/2000. Originally, the system had been equipped with a 11/23 CPU board (as the logo says), but it was upgraded later on with a 11/73 CPU board. The system comes with a lot of peripherals:

Two RL02 drives, one Fujitsu M2312K SMD hard disk drive (87MB), two 8'' floppy drives, a Cipher F880 reel tape drive and a DHV11 communications controller in order to connect 8 terminals.
The operating system installed is RSX-11M Plus.

The second 11/73 system has been built up by myself. I got the KDJ11 board from the nuclear physics institute of my university. So I built up another 11/73 system in a BA23 enclosure for testing purposes.

More Pictures of the PDP 11/73:

                      front-2 The complete configuration housed in two DEC cabinets. The left one contains the qbus-based chassis with the PDP 11/73 CPU and an extension chassis plus an RL02 removable disk drive. The right chassis contains peripherals such as another DEC RL02 drive, a Fujitsu SMD disk drive, two 8" floppy disk drives and a front-loading reel tape drive made by Cipher.
Another view on both cabinets from a different angle.
PDP11/73 front-aside
                      main front Close-up of the "system" cabinet containing the CPU.
From top to bottom:

1) DataRAM qbus chassis housing the CPU- and memory boards plus a DHV11 communications controller.
2) Self-made panel holding the eight serial line connectors of the DHV11 controller
3) DataRAM qbus extension chassis. This one contains additional peripherals-related boards such as the RL02 disk controller, a floppy disk and tape drive controller and an Emulex SMD disk controller.
4) RL02 removable disk controller. Each disk pack can store 10MB on a single 14" disk platter.
5) DEC power controller hidden behind the black panel.
The rear view of the system cabinet. At the bottom, a large fan is installed to garantuee sufficient air circulation.  PDP77/73
Close-up of the "system" cabinet containing additional peripherals.
From top to bottom:

1) front-loading reel tape drive: Cipher F880 which communicates via the PERTEC interface.
2) Dual 8" floppy disk drive custom-made chassis.
3) Fujitsu Chassis holding a Fujitsu M2312K disk drive and its power supply. The disk drive communicates via SMD-interface with an SMD-controller made by Emulex.
4) A second DEC RL02 removable disk drive.
The rear view of the peripherals cabinet.
PDP 11/73
Close-up of the DataRAM qbus chassis front panel. The sticker indicates that this system was originally equipped with a 11/23 CPU which was later replaced by a faster 11/73 CPU (J-11 chip). This upgrade was commonly done by DEC for the 11/23 line of PDP-11 computers. I never came across such DataRAM chassis anymore and uploaded its documentation to to make it accessible to other computer enthusiasts.
The Cipher tape drive F880 accepts write densities of 1600 and 3200 BPI. The latter is rather uncommon. Most reel tape drives used from the eighties to the early ninethies supported 1600BPI and 6250BPI (GCR-encoding), but not 3200BPI.