digital equipment corporation · maynard, massachusetts
My PDP-8/I at VCF East 5 (2008)

The retro computer hobbyist group MARCH hosted the Vintage Computer Festival East 2008 exhibit. I brought a PDP-8/I Computer with 8k core, along with AX08 laboratory peripheral, DF32 Fixed head disk drive, PC01 High speed paper tape reader/punch, ASR-33 Teletype, Tektronix 611 and 603A storage tube monitor, Calcomp 563 incremental plotter, and PT08 serial port, and VT320 terminal for my exhibit. The PDP-8/I was the third model of PDP-8 computers. I also brought a DECmate III which was the last of the PDP-8 line of computers.

I was showing how the AX08 could capture a signal from a signal generator or a microphone, display it on the Tektronix monitor, and plot it on the plotter. I also installed the extended arithmetic element (EAE) for the 8/I so I could run spacewar this year. To install the EAE 8 wires needed to be removed from the backplane and 25 cards installed. See the pictures below. Since the machine has no particular provenance and installing options yourself was done when machines were new I decided that removing the backplane wires was ok. I try not to make changes which can't be reversed to the machines.

Spacewar needs a monitor which settles faster than the 70us of the 611 so I used the 603A for it. The 603A CRT is bad so it doesn't work well as a storage monitor but worked fine as a normal monitor.

I also had games people could play using the teletype. Using the PDP-8/I internal serial port and the PT08 with the VT320 terminal I could also run multi user basic (Edusystem 20).

The other item new this year was I completed a board for the DF32 disk drive that simulated having additional DS32 expander disks attached. For the demos I wanted to run I needed more space than one DF32 provided and the DF32 wasn't reliable. The original intent was to use the board to rewrite the timing track so hopefully the DF32 would be reliable and then use the board as three additional drives to give me enough space (128k words). The moving of the card cage caused the cable to the head to delaminate so the DF32 platter can't be used until I can fix that. I used the board instead as 4 DS32 expanders. Information on the board here

Things went pretty well this year from the failure standpoint. I only had to replace a transistor that drove one of the front panel bulbs shortly before leaving. The VT105 terminal when I turned it on only displayed a line across the middle of the screen. A whack on the side got a full display but it was jittery so I brought the VT320. The Tektronix 611 monitor also failed in the last 10 minutes of the show.

The following picture links also have descriptions of what is shown in the pictures.

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PDP 8/I and peripherals (678K)  DECmate III and VT320 (725K)  8/I rack (1.0M)
Showing off my toys (681K)
Loading in the rain (1.1M)
PDP-8/I Backplane (1.4M)  EAE wires removed (683K)  Parts replaced this year (956K)
DS32 emulator boards (921K)  back of boards (963K)  DF32 cable (817K)

These people take better pictures than me. This site also has some nice pictures of my exhibit along with the other exhibits. more VCF pictures and still more and the last picture link

Feel free to contact me, David Gesswein djg@pdp8online.com with any questions, comments on the web site, or if you have related equipment, documentation, software etc. you are willing to part with.  I am interested in anything PDP-8 related, computers, peripherals used with them, DEC or third party, or documentation. 

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