MARCH/InfoAge PDP-11/20 System and Exhibit
Created Oct 7 2007. Last edit Sept 9 2008. Herb Johnson
Index to this Web page
Current exhibit status
MARCH, VintageTech and InfoAge
Introduction to the Greenough 11/20 collection
Questions about the system and collection
What does MARCH have?
How was it used and programmed?
How was the 11/20 operated?
Can the 11/20 be restored and run today?
Web links for more information
Contributors to Web page and exhibit
Early Exhibit Plans and progress
Other DEC systems at MARCH
Contact info
MARCH/InfoAge Exhibit progress
As of Sept 9th:
On September 13 and 14 2008, MARCH plans to have a computer show and the public opening of their new Museum facilities at InfoAge.Check this link for more information. The PDP-11/20 described here will be one of the Museum exhibits, and I (Herb Johnson) developed that exhibit for MARCH. The posters in the exhibit are based on the contents of these Web pages. The 11/20, some artifacts, and videos of computer operations will also be on display.
Here is a representation of the MARCH PDP-11/20 exhibit - as presented to MARCH - as a set of HTML and image documents. That Web page shows images of the artifacts and posters for the exhibit. The images have links to larger images, videos, documents, etc. of the actual exhibit. The videos were to be shown at the exhibit, on a donated Linux-based modern computer.
The actual poster documents were specified by MARCH to be done in Microsoft Word, to be printed by MARCH at InfoAge on a poster-sized color printer; or printed at Kinko's (FedEx Office).A specific InfoAge header and footers was required for all posters. The poster files were given to MARCH in late August 2008. The contents of these PDP-11/20 Web pages were also given to MARCH at that time, to be displayed on their Web site. We will provide links at this site (retrotechnology.com) when that occurs.
Contributors: The exhibit artifacts, video-display computer, and all documents were delivered to MARCH, except for two paperback books from Paul Popelka, and paper tapes for display. David Gesswein provided the videos, and a PDP-11 card on loan for the exhibit. Joe Giliberti donated a DEC PDP-11 handbook as well. Much of the content about the original use of this 11/20 was written by the donor, Leighton Greenough, who bought it for the federal NBS (now NIST) in 1970. Thanks to all for their contributions and help.
For reference: MARCH Museum posters at InfoAge will be similar to this LARGE poster document from the upcoming Mauchly exhibit as provided to me from MARCH. The directory linked here, contains Word documents for the 11/20 posters and associated image files.
Herb Johnson
MARCH is the Mid-Atlantic Retro Computing Hobbyists, with facilities at the InfoAge Science Center in Wall, NJ. This Web page (on my retrotechnology Web site) is a short-term way to let MARCH members know what they have, and what went on with that project. In due course this will migrate to a MARCH Web page.
The MARCH Web site is at this link.
The InfoAge Web site is at this Web link.
This is the Web page for the "Vintage Computer Fest - East 5.0"s how as sponsored by VintageTech>
The MARCH Yahoo! maillist is at this link.
![[11/20 front panel]](11_panel_2_sm.jpg)
In August 2007, MARCH acquired a PDP-11 system. When I came to InfoAge
to help Evan set up the new exhibit and storage rooms, I saw that it was an 11/20, with a
largely COMPLETE collection of manuals, schematics, and even the paper-tape operating system. I saw right away that this could be the basis for an exhibit of 1970's "state of the art" for DEC minicomputers, even without running the system. Evan agreed (after some consideration) and, with encouragements from other MARCH members, I'm working the details.
In addition, MARCH soon found that this system was part of document scanning systems developed by the US Government's National Bureau of Standards (NBS, now NIST) from the 1950's through the 1990's. This particular system was donated by M Leighton Greenough, who developed systems used those systems at NBS and later as a consultant. He eventually purchased it and continued to do similar scanning work for the US government. Mr. Greenough was kind enough to write a description of his history with these system and provide photos, which are now available on this Web page. This particular PDP-11/20 was used for evaluation of experimental scanning techniques and not for production scanning.
This 11/20 donation includes the original 1969 distribution of DEC's paper tape operating and development system, including paper tapes and manuals. A description of the DEC paper tape software system and its console of switches and lights, is on the Web pages linked in this section.
- Herb Johnson
How did MARCH acquire the PDP-11/20?
![[11/20 system and docs]](dec_n_docs_sm.jpg)
Here's how Evan Koblentz, MARCH Board Director, described the acquisition, including details from the original owner:
"We're very lucky: the guy who donated it sent me an interesting blurb about the machine's history. He emailed me on June 27, saying that he learned about MARCH
at the recent Trenton show." He dropped off the system early in August. Here's his email: - Evan Koblentz.
"This machine was bought by the National Bureau of Standards in the early
1970s for a project I was working on. I modified it a bit to create an
interface to a flying spot scanner. After some use it was declared
surplus upon my retirement in 1976. A year later the U.S. Postal Service
Research Laboratory acquired it and commissioned me to modify the scanner for
their work. A memory expansion unit was there added. In 1986 the USPS no
longer needed the equipment and accepted my unsolicited bid for purchase
of the entire system, including the computer, scanner and other
associated equipment. The computer has been on a shelf in my house ever
since. Now I would like to find a good home for it." - Leighton Greenough
In a later communication from Greenough, he affirms that "although incorporated
in a system compatible with [Census] specialized documents, [this computer] had no
connection with [the Census Bureau] beyond evaluation of experimental scanning techniques."
Components available and condition (from Greenough)
Main chassis without power supply , in rack mounting
Power supply for above, H720e
Expansion memory: Plessey 1116 B, Core (16k, 16-bit words)
Bus cables: 6, 9 and 15 feet
Boxes, approximately 15x22x4 (2) of manuals
Boxes of DEC (in trays) and custom programs
Miscellaneous DEC circuit boards
There is no Teletype console
Main computer chassis is in apparently excellent condition. The power
supply (included) has been separated from the main chassis for
convenience in handling.
PDP-11/20 system with a 1/20/72 list of boards on the back as follows:
KA11 CPU
KW11L or KY11L (programmer's console (front panel))
RL11A or DL11A (serial and clock)
PC11 (high speed paper tape controller?)
three MM11FX modules, 8K bytes? 16K bytes each
H227E (power?)
Three boxes of paper tapes (two sets of DEC system stuff, some DECUS stuff);
two boxes of manuals (about two sets)
box with core memory module, Plessey Microsystems PM-1116-B ? with manuals
box with Unibus cables
white binder of manuals
two external power supplies (one in box)
The boxes have old lables such as "manuals from NEWMAN, 1977"; "paper tape programs from USPS Mach. FOSDIC VI". As of Aug 3 2008, the boxes have yellow Post-it notes saying "11/20 Greenough".
A detailed but partial inventory of the hardware, software, manuals and paper tapes is on this linked Web page. It also has a description of 2008 correspondence with Leighton Greenough about the exhibit and Web site. He contributed text and photos which were included on these Web pages and on the exhibit posters. Thank you.
Card positions in 11/20: front panel to far right
![[inside of 11/20 bus]](11_cardcage2_small.jpg)
<-----------(bus cabling, M920 jumper blocks, resistive terminators) ---------->
G225 M1091 G225 M1091 M825 M823
H207 G226 G226 M7290 H207 G226 G226 M7290 M792 M780 M824 M822 M224 M820 M725 M724 M726 M728 M727
YA
G102 G102 M7290 G102 G102 M7290 M792 M780 M824 M822 M224 M820 M725 M724 M726 M728 M727
YA
G102 G102 G102 G102 M792 M105 M225 M821 M224 M820 M725 M724 M726 M728 M727
YA
H207 G226 G226 G103 H207 G226 G226 G103 M792 M7820 M225 M821 M224 M820 M725 M724 M726 M728 M727
YA
PDP-11/20's like this system, with optical and other equipment, was developed and used by the NBS in the 1970's, to scan documents for the National Census. In the 1980's they did similwar work for the US Postal Service. This particular computer was used for development and experimentation. A description of the history of the NBS FOSDIC system line, with photos of use, was provided by the original developer. That history is now available on this Web page. Further Web pages references for FOSDIC are on that Web page.
The NBS or National Bureau of Standards, is now the National Institute of Standards and Technology (NIST) at nist.gov. NBS and NIST research provided technological leadership in many areas, and also established and maintains standard measures. A general description of how they developed massive optical scanning technology such as FOSDIC for the Census Bureau is at this link.
Programmers studied DEC's "PDP-11 Handbook" to program the 11/20, to operate its elaborate console or front panel, and to use the programming tools sold with it. Here's some exerpts from that handbook:
This chapter is the Introduction
The components of the PDP-11 were in this chapter
Use of the front panel or console was described in this chapter
This chapter described the Paper Tape Operating System, the manuals and paper tapes which are in our collection. See the "inventory" for a list of them.
To program the 11/20, the minicomputer had to be powered up, and programs loaded in. Initial loading, as well as diagnostics and tests, were done through the front panel. Then programs were loaded from paper tape or hard disk. The computer was often operated from a Teletype, a printing terminal. The section on "operation" describes these methods and devices.
The 11/20 computer itself has no programs in it, not even programs to read programs from devices like the Teletype or disk drives. To load the first programs when the computer is started up, the "console" front panel was often used; the console is also a diagnostic tool for repair and maintenance. A small program called a "boot loader" could then load other programs from those devices. Programs had to be loaded in, one at a time; the program was run, maybe producing a result which was output. Then another program was run, and another, and so on. For applications like the FOSDEC, where the same program was always used, the "loader" programs would be stored in ROM (fixed memory), and they'd load the appropriate programs from disk.
Otherwise, for program development, the PDP-11/20 was often sold with a Teletype, a printing terminal with its paper-tape reader and punch. Optionally the 11/20 could have a Remex brand high-speed paper tape reader and punch. "Paper tape" contains data and programs; it has sets of 8 holes in rows, and are read or punched by rows to represent "bytes" of data or a single character of text in "ASCII" code. In the era of the 1960's, before hard drives were common and before floppy drives were available, paper tape was sufficient to hold modest amounts of data and programs.
DEC provided a "Paper Tape Operating System" with this PDP-11/20.
Photos and discussion are in this chapter exerpt from the DEC 11/20 User's manual.
Operation of the 11/20 at start-up: the front panel
The PDP 11/20, like many minicomputers of the 60's and 70's, had a "front panel" called a console which was used to access the computer and program it at the binary (bit) level, one memory location and one instruction at a time. Our 11/20 console is described in detail in the "console" manual exerpt described above.
Absent an operating 11/20 system,
we provide a 3MB .AVI video of the operation of a DEC PDP-8 console. The PDP-8 is a smaller "cousin" of the PDP-11, similar in age and function but which runs different software. The video shows the operation of that console, in a manner similar to the 11/20's console, to start up the computer. A description of the front-panel operations in the above video is in this Web page. The PDP8 boot video from David Gesswein is available on his site at this Web link.
Operation of the 11/20 after startup: the Teletype
It was common to operate PDP 11's with a Model ASR-33 Teletype. This was a person-operated printing terminal with keyboard, which could also read and produce paper tapes. "Paper tapes" were described briefly as part of the operation of, and software for, the PDP-11/20. The Teletype printer is controlled by either the paper tape reader, or data input on the Teletype serial line. The Teletype keyboard, or the Teletype paper tape reader, sends data output on the Teletype serial line. "Serial" means the binary data is sent on a single wire, bit by bit and byte by byte, in a sequential or "serial" fashion.
Complete operation of a Teletype with a minicomputer is shown in a 3-minute, 21Mb AVI video. This video from David Gesswein is available on his site at this Web link. Additional videos as below, will show details of the Teletype's functions. The operator uses the Teletype's keyboard, printer, tape punch and tape reader to interact with a PDP-8, an older DEC computer than the PDP-11/20. The operations shown are similar to those with the 11/20 with the same Teletype. A detailed description of the user's operations in this video is in the linked text file.
Operational features of the Teletype: print text, read and write punched tape
The Teletype prints text, either as received from the serial line, or "echoed" from the keyboard, or from ASCII text read from the paper tape reader. A 3MB .AVI video of the printer at this link. The printed text is a FORTRAN program.
This video from David Gesswein is available on his site at this Web link.
The model 33 Teletype can also punch a paper tape with an ACSCI or binary pattern of eight bits at a time. This link is to a 2Mb .AVI video of the Teletype punching a tape. In the audio, you can hear both the punch and the printer in operation. Note the paper tape has rows of eight holes plus a small hole called the "feed hole", which is used to align or feed the tape. This video from David Gesswein is available on his site at this Web link.
The model 33 can "read" the paper tapes it punches. This is shown in a 1MB .AVI video. The tape is fed over the reader, which has a spiked wheel to pull the tape over the reader. The small line of holes in the center of the tape are the "feed holes". This video from David Gesswein is available on his site at this Web link.
These videos were produced and provided by David Gesswein of pdp8online.com and are used here with his permission. Thank you.
It takes considerable skills and experience to restore a forty-year-old computer to full operation. That includes knowledge about technolgies no longer in use, and skills to repair digital and analog electronics down to resistors, capacitors, transistors and integrated circuits. One example of such work today is David Gesswein's PDP-8 collection of running computers.
Here is a link to an example of one of his repairs..
MARCH member Bill Degnan acquired a PDP-11 in 2008, and is learning how to work on it. Check his blog Web page on vintagecomputer.net for details about Bill Degnan's PDP-11/40,including UTube videos.
DEC was purchased by Compaq Computers. Compaq was purchased by HP. In 2008, all I could find on HP's corporate site, was references to Compaq. Some of their pages reference DEC systems of the 1990's and later, which are or were supported "recently".
There are many Web sites devoted to DEC's minicomputers of the 60's and 70's and beyond including the PDP-11 line of minicomputers. They offer far more support and description than these Web pages. A Web search will find them.
Thanks to David Gesswein of pdp8online.com for permission to use these videos, which he produced. He created new videos and text descriptions in 2008, to support this exhibit and Web page. The PDP 8/I and ASR-33 Teletype are owned, maintained and described by him. These and other videos are on his Web site.
There is a Web archive site which links to other archive sites which have manuals on-line.
The MANX Web site has its own database, to provide links to some of the on-line manuals for the PDP-11/20.
What do these boards do? Some Web sites with information about DEC boards of this sort are:
a field-guide list of DEC modules
by function is at this site
and the module list is also at this site
Schematics per board are at the pdp12.org Web site.
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.
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 Paul Popelka and Joe Giliberti, who donated DEC PDP-11 handbooks for public use at the exhibit.
Thanks to MARCH member 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 from Aug 2007 through September 2008. Much of this material will be supported and hosted by MARCH after that period, including a change of Web site.
This is an account of the development of the 11/20 exhibit for MARCH. See the top of this Web page for the status of that exhibit.
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.
Evan added another consideration: it can be a short-term exhibit, one of a number of "member's interests" exhibits taken either from our collection, or from a member's collection. See his comments below via the Web link.
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 and is now on another Web page. 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.
March-April 2008: Added information about MARCH's other DEC computers, notibly a PDP-8 "straight 8" acquired in mid-April.
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. Mr Greenough provided more information about the FOSDEC scanner optics, which was added to this Web site; and related notes.
June 2008: videos from David Gesswein, made for this exhibit, added to this site.
July 2008: Prototypes of the MARCH Museum exhibit posters for the 11/20 are discussed at this link. MARCH plans to have a computer show and the public opening of their new Museum facilities in mid-September. Check the MARCH Web site for details of the event.
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.
late Aug 2008:The exhibit was completed, except a transparent cover for the 11/20 was not produced. All Greenough documents, copies of the Web pages and poster Word files, were transferred to MARCH and MARCH recieved copyright for them. Items or content loaned to MARCH were identified. Content produced by others (not Herb Johnson) was identified so that MARCH could resolve copyright, updates, and attributions with the owners of that material. The exhibit was set in place; a computer was donated to show the videos; MARCH was to produce the actual posters for the exhibit.
The current status of the MARCH exhibit is described at the top of this Web page.
Early Comments from MARCH members & officers
The comments below were from Oct 2007. For more recent comments, check the MARCH Yahoo! Web site.
MARCH President Evan Koblentz responded in the context of plans for our first two exhibits,
as he described earlier: "I believe this [first exhibit] room
can hold four exhibits. For now, just to reiterate, our first
two-and-a-half exhibits will be "Computing in the Military", "Computers
of the Region", and "Computer History at InfoAge"; that third one is
sort of a miniature exhibit so I'm counting it as half."
After reading the proposal, Evan posted: "I just think it makes more sense to save our
best DEC items for the exhibit on minicomputers, and/or other
to-be-determined exhibits, instead of using it for this first exhibit on
local products....But I suppose we can make a THIRD "first" exhibit, which
would just be a "best of the rest of our collection" while we continue
planning and restoring things. And the PDP-11 certainly would fit into
that category too."
He continued with another consideration: "In addition
to just showing off some of our more fun systems, this is a good way
to keep everyone interested while the club
focuses on other current exhibits. For example, say the current
under-construction exhibit in six months from now happens to be about
data storage, but you don't care much about data storage ... you could
do what Herb's doing and work on a pet project for the "best of"
exhibit. We can also use this exhibit space as a way to highlight
members' personal collections, and we can rotate that space frequently.
Again, for example, say there's a month when Andy is spontaneously
inclined to show off his Sony SMC-70, or perhaps Mark will want to do a
mini-OS2 exhibit around Warpstock time -- no problem, they'd just use
part of our exhibit space designated for this purpose. The more I
explain the idea, the more I like it ... keep everyone involved, use
more of our physical exhibit space, vary the exhibits beyond what MARCH
owns ... sounds good right???"
MARCH Treasurer Jim Scheef said: "Using the PDP as a static exhibit (at least to start) sounds like a great idea. It has a lot of substance with its size, the manuals and many learning opportunities with the tape OS (I'd never heard of that), etc. Do you envision signs or display cards to explain things? I'm listening..."
Member Bob Applegate noted: "We SHOULD be interested in DEC stuff.
While Maynard [MA, the original home city of DEC] might not be considered Mid-Atlantic, DEC was
certainly a major player in the early days. Reading through the
first issues of Dr Dobb's, lots of people
discussed ways to run PDP-8 and PDP-11 software on their micros.
DEC had a big impact on a lot of us folks back in the 70s."
MARCH Vice President Bill Degnan sent some encouragements privately and may put the word out to others with DEC interests. (Later on, he bought a PDP 11/40 and he's displayed it on his Web site.) Member John Allain has also contacted me and wants to work with MARCH's DEC equipment.
MARCH member and PDP-8 owner David Gesswein has provided videos of his use of his PDP-8 as examples of how the PDP-11 was used.
Dan Roganti of MARCH suggested: "Something that always appealing at a computer museum, I think, is having one of these minicomputer circuit cards mounted in a glass display (a spare board that is). There's nothing more interesting to visitors that getting to see the actual circuitry up front and in person (even though it's not running). And maybe with a little placard with a short description of how many transistors were possible or a speed comparison of the circuit card." Dan, we'll show a DEC card from a non-critical collection of loose DEC cards, and let visitors handle it.
Emails from others
Paul Popelka said he has an 11/20, and he's working on a MM11-F core memory card, so he's looking for documentation. Later on, he provided two DEC manuals for the exhibit. Thank you.
This is not a comprehensive list. It is here to answer a simple question: "What else does MARCH have in PDP-11's"? - Herb Johnson
11/05 boxes:
![[front of 11/05]](11_05_front_sm.jpg)
photo of card set for 11/05
detailed edge-on photo of 11/05 boards
close photo of card ID's
photo of front of 11/05
photo of 11/05 card list
photo of another 11/05 stacked elsewhere
In late April, MARCH recieved a PDP-8 with plotter and TTY from Claude Kagan, of SAM-76 fame, and courtesy of the RESISTORS computer club of the 1960's and 70's. Follow the link for details.
Tom Owad's VAX and DEC graphics system - last updated April 14 2008
Tom provided to MARCH, a DEC 11/23 system with graphics capability, and a VAX 750 system. Follow the link for details.
Other DEC PDP-11 hardware of MARCH - last updated April 14 2008 Herb Johnson
Here's some June 30 2007 images of MARCH's DEC PDP-11 hardware, from my photo archives of some work done prior to painting. No guarantees whatsoever, that I correctly identified anything or everything.
11_40_3.jpg an 11/10, a DEC Laboratory system, an 11/40<
11_05_1.jpg a DEC Laboratory system, an 11/40
RM80.jpg two RM80 drive cabinets under some non-DEC object
11_40_1.jpg 11/10, 11/40 as above, plus two drive cabinets<
PE_MSM300.jpg Perkin Elmer branded disk drive, may be DEC drive
RK05.jpg two RK05 drives, front and back
RX01.jpg RX01 diskette drive, loose floppy controller card
RK05_2.jpg three RK05 drives to left; blue drive in center; DEC CPU to right?
RK05_1.jpg three RK05 drives
To email MARCH or InfoAge, see the MARCH Web site as described at the top of this Web page. To contact Herb Johnson, look below for email info. If you are interested in contacting Leighton Greenough, send a message to Herb Johnson.
Contact information:
Herb Johnson
New Jersey, USA
To email @ me, see see my ordering Web page.
Copyright © 2008 Herb Johnson
![[11/20 front panel]](11_panel_2.jpg)
![[11/20 system and docs]](dec_n_docs.jpg)
![[inside of 11/20 bus]](11_cardcage2.jpg)
![[front of 11/05]](11_05_front.jpg)
