![[11/20 front panel]](front_panel.jpg)
Created Oct 7 2007. Revised May 22 2008. Last edit June 08 2008. Herb Johnson
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.
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 we have, and what's going on with this project. In due course this would migrate to a MARCH Web page, and will be considered for an exhibit of this system and its history. The MARCH Web site is at this link. The MARCH Yahoo! maillist is at this link.
- Herb Johnson
![[11/20 system and docs]](dec_n_docs.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.
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
The boxes are labled "manuals from NEWMAN, 1977"; "paper tape programs from USPS Mach. FOSDIC VI".
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.
The 11/20 itself when sold had no programs in it. They 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. To load the first programs when the computer started up, the "console" front panel was often used; the console is also a diagnostic tool for repair and maintenance. For applications like the FOSDEC, where the same program was always used, those programs would be stored in ROM (fixed memory) or loaded automatically from paper tapes or disk drives.
For program development and for use, the PDP-11/20 was often sold with a Teletype, a printing terminal with its paper-tape reader and punch; and optionally with 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 before hard drives and floppy drives, paper tape was sufficient to hold modest amounts of data and programs.
Programmers studied DEC's "PDP-11 Handbook" to program the 11/20, and 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.
You can get some idea of how a Teletype was used, and how our 11/20 was programmed, by watching the video on this Web page which shows the use of a Teletype with a PDP-8. A description of that video is in this text file. Other links on that Web page provide discussion of that computer session. For example, there is an annotated page of text from a terminal session with that PDP-8 computer, on this Web page at that site. Again, it's similar to what was was done with the 11/20 system. Photos of paper tapes are in the description above of the Paper Tape Operating System.
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. On this linked Web page, near the bottom, is a link to a Real Media video of a PDP-8 console. It shows the operation of that console, in a manner similar to the 11/20's console, to start up the computer. A description of that video is in this text file. Our 11/20 console is described in detail in the "console" manual exerpt described above.
Thanks to David Gesswein of pdp8online.com for permission to use these videos, and for creating new videos in 2008 for this exhibit and Web page.
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 site for his PDP-8 collection of running computers, at pdp8online.com. A recent example of the kinds of repairs needed is on this Web page of his. Thanks to David for permission to reference his work.
There are many Web sites devoted to DEC's minicomputer products of the 60's and 70's and beyond including the PDP-11 line of minicomputers. A Web search will find them. I'll provide a few Web links below but by no means a comprehensive list of links.
There is a Web archive site which links to other archive sites which have manuals on-line. The MANX Web site has a search engine to find some of those on-line manuals for the PDP-11/20.
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, which referenced DEC systems of the 1990's and later.
Herb Johnson with the 11/20
Evan Koblentz, co-founder and current Board President of MARCH
The 11/20 with a VT-100 terminal (not part of Greenough's donation) and docs and software (paper)
The 11/20 front panel
More docs, power supply, 11/20
docs and media:
photo of MACRO-11 assembler listing
photo of box of rolled tapes, handbooks
photo of a collection of PDP-11 brochures
photo of a colorful manual cover
photo of typical manual cover: DL11-W
photo of schematic for DIODE 128 byte memory
photo of handbooks, a manual, some rolled tapes, a PDP-11 programming card
photo of 1971 DEC installation report for one system
photo of typical long binder for hardware engineering manuals
photo of one of MANY sets of folded paper tapes for the PDP-11
photo of three segments (of 10!) of a PDP-11 programming card
photo of one of many engineering schematics
sales brochures, prices and specifications
1971 groovy sales image of PDP-11 installation: from price list brochure
photo of PDP-11 site in LegoLand?
image of PDP-11 description
image of PDP-11/10, /20 specifications
photo of 1971 price sheet: system, mass storage
photo of 1971 price sheet: disk, cards, papertape devices
![[inside of 11/20 bus]](11_bustop2.jpg)
photo, open "top" showing backplane from rear
photo, list of cards installed in 1970
photo, side fans
photo, internal cables
photo of 3X3 Molex connector on cable
photo of 8-pin Molex connector on cable
photo of 37-year-old foam cushioning
photo of 11/20 card set
photo of 11/20 card cage interior
photo of M724 chips on "rear" edge of card
photo of top front of backplane where Unibus would be cabled
photo of cable going into M792YA card
photo of M821 chips on "rear" edge
photo of G102 chips on "rear" edge
close photo of top front of backplane where Unibus would be cabled
photo of M792 diode memory
![[inside of 11/20 bus]](11_cardset.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
An inventory of the hardware, software, manuals and paper tapes is on this Web page.
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.
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. 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.
Paul Popelka says he has an 11/20, and he's working on a MM11-F core memory card, so he's looking for documentation. I'll pass along any responses.
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
photo of card set for 11/05 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 provided to MARCH, a DEC 11/23 system with graphics capability, and a VAX 750 system. Follow the link for details.
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<Emails from others
Other DEC systems at MARCH
11/05 boxes:
![[front of 11/05]](11_05_front.jpg)
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
RESISTORS\Kagan PDP-8 "straight 8"
Tom Owad's VAX and DEC graphics system - last updated April 14 2008
Other DEC PDP-11 hardware of MARCH - last updated April 14 2008 Herb Johnson
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:
Copyright © 2008 Herb Johnson
Herb Johnson
New Jersey, USA
To email @ me, see see my ordering Web page.
