DEC PDP-9

System Number 319

The PDP-9 was a follow on to the highly successful DEC PDP-7 series of computers. While there were some differences, one of the PDP-9 system utilities would convert PDP-7 programs to run on the PDP-9. Input was by paper or magnetic tape.

This system was purchased by Max Levy Autograph in October 1968 and shipped to Concord Controls who designed and built the controller for the 60" photo-plotter. This was one of the largest such devices in the world. It was used to prepare glass for etching as filters and measuring templates. The photo-plotter rested on a five foot thick granite slab, with supports set in bedrock. The PDP-9 and photo-plotter was then shipped to Philadelphia, PA and ran 24/7 from 1968 to the summer of 1999. When the memory limitations of the PDP-9 caused problems with programming they bought a PDP-11/23 and connected it to the PDP-9 through a special I/O controller that let the PDP-11/23 control the PDP-9.

We were contacted by Ted Heimberger, the person who operated this system for 30 years. He filled us in on much of the history of the system and will come to the RICM for a visit. The notes that are taped to the front of the system are his.

This PDP-9 was located for the RICM by Kevin Stumpf, and donated by Max Levy Autograph of Philadelphia, PA. A total of 445 PDP-9 systems were produced, and so far, only nine are known to have survived.

The current locations of these nine include a PDP-9 and a PDP-9/L in California, one in Australia that came from La Trobe University in Melbourne, one in Germany, one in Great Britain, two in France, two in Sweden and a new one #203, and of course our own, seen below. Parts of #209 that was delivered to Australia Iron & Steel were recently found. There are lots of details on the developers of the PDP-9 here.

Apparently the design of the ROP Control Memory in PDP-9 systems caused lots of problems. Lichen Wang from SLAC developed an improved design that proved more reliable. The description is here.

8,192 words of core memory with an 18-bit word length

1.0 usec cycle time

Real-Time Clock

Operator's Console

300 cps Paper Tape Reader

50 cps Paper Tape Punch

10 cps Console Teleprinter, Model KSR-33

The processor cost $35,000 in 1968.

The TC59 tape controller cost $10,000.

The TU20 tape drive cost $12,000.

The cost in 2020 dollars of this system would be $400,886.

With the TC02 DECtape controller and TU55s drives that we added the total is $502,513.

The PDP-9 Console.

The PC09 Paper Tape Reader/Punch and a TU55 DECtape drive are located above the control panel.

The PC0, S/N 863, contains a PC02 Paper Tape Reader and a PC03 Paper Tape Punch.

The cabinet to the right contains 2X TU55 DECtape drives, the TC02 DECtape controller, and the TC59 Magnetic Tape controler.

The magnetic tape drive to the left is a TU20 7-track drive.

If the system was run 8 hours per day, this shows 20 years of run time.

The Core Memory Controller serial number matches the maintenance contract.

The Processor serial number tag is missing.

The I/O controller serial number also matches the maintenance contract.

The PDP-9 system console.

The original configuration of the PDP-9 according to DEC.

There is a date of January 17, 1968 on many of the CPU fans. That is about right for the manufacturing date of this system.

The official production run was 445 PDP-9 systems. Additional systems were built on special order after production ended.

The PC0 paper tape reader/punch is S/N 863.

Rear view of the PDP-9 Processor.

Yellow wires are factory installed. Blue ones are design changes, probably made in the field. The green wires could be design changes or additions.

A rear view of the system console. This was taken before restoration.

Front view of the system chassis.

The upper 1/3 is 8kW of core memory. The missing boards are for the Parity option that was not ordered.

The middle 1/3 is the Processor. The missing boards are for the EAE option that was not ordered, but we will install so we can run UNIX and Spacewar!.

The bottom 1/3 is the I/O Controller. The missing boards are for the KF09-A Automatic Priority Interrupt, the KP09-A Power Failure Detection, and the 34H-0 display options. We will install the 34H graphics controller so we can run Spacewar!.

Front view of the TC59 Magnetic Tape Controller. This can control TU10, TU20, and TU30 Magnetic Tape Drives. This system has a 7-track TU20 drive.

The image below is of the TU20, 45 IPS, 7-track tape drive that was attached to the PDP-9. It supports 200, 556, and 800 BPI tape densities. From the label on the rear of the transport it appears to be an HP 7975A made for DEC using IBM's tape velocity fluctuation damper patents.

The capstans and read-write head on the TU20 Tape Drive.

The 7-track read-write head on the TU20 Tape Drive.

Rear view of the TC59 Magnetic Tape Controller for the TU20 7-Track Magnetic Tape Drive. The empty slots at the bottom right are where the I/O cables are installed.

The HP 7-track tape drive with DEC electronics to make it a TU20 Tape Drive.

This is the board that holds the microcode for the processor.

A pulse is sent through one of 64 wires and microcode bits are coupled through the transformers and latched into flip-flops.

This is the board that caused lots of intermittent problems in the late 90s.

The DEC 709 Ferroresonant Power Supply.

It makes 3A of +20VDC, 5A of +10VDC, 20A of -15VDC, and 10A of -30VDC.

You can see some evidence of a past diode block failure.

We have a second 709 Power Supply that needs to be repaired and installed before we can use the paper tape punch.

This is a custom made chassis that allows a DEC PDP-11/23 system to control the PDP-9 and to download software and data at high-speed.

The TC02 DECtape controller is S/N 5048.

Charles Lasner donated this TC02 DECtape controller for 18-bit DEC systems.

Now that this is this working, we can run a real operating system on the PDP-9.

We borrowed three TU55 DECtape drives from the PDP-8/I for the PDP-9.

This TC02 display panel is very similar to the TC01 display panel on the TC01 in the PDP-8/I.

The DATA BUFFER will display 18 bits, instead of 12 bits on the TC01.

The larger DATA BUFFER display required moving other indicators to make room for the additional bulbs.

We installed the TC02 DECtape controller above the TC59 1/2" Magnetic Tape controller.

Mattis Lind made an Arduino interface for his DEC PC04 paper tape reader. He read some of his PDP-9 diagnostic paper tapes and emailed the paper tape images to us. We sent the paper tape image through the serial port on a PDP-8/S to a paper tape punch to recreate the paper tapes. A video of the paper tape reader in action is here.

A DEC PDP-9 advertisement from the 1960s.