Contributors to and history of the PDP-11/20 Exhibit

Page revised Aug 30 2013. This material licenced from MARCH by Herb Johnson. This is a link back to the home page of the 11/20 exhibit.

Contributors to the exhibit

Thanks to Leighton Greenough for his generous donation of the 11/20 and materials, for his subsequent descriptions and photos of FOSDIC history, and his suggestions about the contents of these Web pages. He corresponded with me in 2008 and provided the bulk of information about FOSDIC and the immediate history of the PDP-11/20. Thanks for his contributions, encouragments and good will. Mr. Greenough died in about 2011.

Thanks to David Gesswein for developing new videos of his PDP-8 and Teletype model 33 in operation. Those videos are used here and in the exhibit with his permission. He also loaned a PDP-11 card and paper tapes for the exhibit. David made considerable efforts to produce these videos and to discuss them with me.

Thanks to Bill Degnan, for providing links to his 11/40 videos. He provided useful review of this work. Jeff Jonas provided review and discussion of the "minicomputer" poster, and contributed to its content.

Other persons who provided comments and suggestions include Jack Rubin, Evan Koblenz, John Allain, Jim Scheef. Thanks for their interest.

These Web pages and poster contents were otherwise developed by Herb Johnson of, from Aug 2007 through September 2008. The exhibit was shown and then dismantled, and the Web pages produced were not maintained on MARCH's Web site. I (Herb Johnson) have displayed them on my Web site.

Exhibit development history

It may be informative to see how an exhibit is put together. Here's my notes about creating this exhibit. - Herb Johnson

Herb Johnson late Aug 2007: Here's a straightforward proposal for a "static" exhibit. First off, the computer would NOT be powered up or running - that may come in time, may not. It will be a "static display" of the system and its documents, as a "here's computing of the 1970's" exhibit. It shows what could be done without hard drives or even floppy drives! And, how minicomputers were used in the period.

Most of such an exhibit would be the items themselves; the rest would be photos and interpretive text to describe use and so forth. Some wall space for poster boards with text and photos, and space for the computer and samples of its documents, paper tapes, and so on. THAT's the basic idea, nothing elaborate, and nothing needs to run. Maybe, with interest, we can get some guys to get a '11 to light up, run some code.

I said "I will take some time to develop this idea, write some text, cut up some photos, lay it out. That can be done in a few days over a few weeks, I will do it on a (non public) Web page on my site. MARCH can look it over and we can talk about it and show work as it occurs." This Web page is a result.

The initial tasks are to inventory what we have in more detail, with more photos. And, to gather more info about how it was used by the Post Office and NBS. That dovetails very well with "computing of the 70's", as I had hoped. Lucky us!

Early Oct 2007: A preliminary list of items is complete, but needs to be verified. A photo survey of the cards and inventory has been done and is on-line. The card list should be identified by function. We also need to know how to connect the power supply, and an apparent serial connector needs to be identified.

Feb 2008: Mr. Greenough mailed to Herb Johnson a CD of images, some nice glossy photos, and a four-page text and cover letter. The text describes his experience with and history of FOSDIC development. That material was scanned and lightly edited. MARCH is discussing how this 11/20, its documents and tapes, the materials from Mr. Greenough, and information on programming, can all be put into an exhibit for the MARCH September 2008 show.

May 2008:Added notes and exerpts from the DEC PDP-11 Handbook. InfoAge now has an HP DesignJet 500 printer which can make professional looking color posters. The PDP-11 cards can't be displayed inside the cabinet, the top of the cabinet only shows a backplane - a photo of the cards will be put on top, instead. [Note: this never occurred.] Mr Greenough provided more information about the FOSDEC scanner optics, which was added to this Web site; and related notes.

June 2008: videos produced by David Gesswein, made for this exhibit, added to this site.

July 2008: Prototypes of the museum exhibit posters for the 11/20 were completed and discussed. the museum plans to have a computer show and the public opening of their new computing museum facilities in mid-September.

Aug 2008:A set of HTML documents were completed which show the proposed exhibit, posters (also as Web documents), and artifacts. The boxes of the Greenough collection were tagged with yellow Post-it notes. Copies of the inventory were placed in some boxes. Better photos of front panel and cards put into Web page and in poster document. Paper tapes and DEC DR11-C provided on loan for exhibit by David Gesswein. Word files given to MARCH to print as exhibit posters.

late Aug 2008:Work on the exhibit and these Web pages completed. Final review and fixes.

mid-Sept 2008: Exhibit posters printed, displayed with PDP-11/20. Paper tapes and displayed DEC card put in glass-covered boxes to display. Linux-based PC set up to show videos of Teletype and PDP-8 to show "operation" like the PDP-11's. Exhibit opened September 15-16 2008 as part of Vintage Computer Festival 2008 - East.

afterwards most of the posters were removed and the loose artifacts removed from the PDP-11/20 display area. One poster on "minicomputers" was retained as part of the musuem's general exhibit of minicomputers. The Web pages did not remain on the museum's Web site. In a few years the computer museum's Web site became essentially one Web page with links; as of 2013 that's the status of that Web site. David Gesswein's Web site continued to use the videos he created.

Copyright this document: © 2013 Herb Johnson, from materials copyrighted © MARCH 2008.