Newbie here

[Robb Bates]

Hi all,

I just ordered my PiDP-11.  I doubt I'll have any issues with the build.

I also understand there are several OSes built in.

I'm just wondering if there is a commonly used one and/or some resources or applications for them.

Any "getting started" other than the official website?

Thanks,

Robb

[Johnny Billquist]

Hi.

On 27/01/2026 16.12, Robb Bates wrote:
> Hi all,
>
> I just ordered my PiDP-11.  I doubt I'll have any issues with the build.

Cool. I think you'll enjoy it.

> I also understand there are several OSes built in.

Well. "Built-in" is maybe too much. But available to download for sure.

> I'm just wondering if there is a commonly used one and/or some resources
> or applications for them.

I think the most used ones are 2.11BSD and RSX-11M-PLUS.

2.11BSD is almost like any modern Unix, being more or less the
grandfather of all of them. If you know your way around Unix systems,
this should be pretty straight forward to use.

RSX is a very different beast. But manuals are online (but it's a *lot*
of reading, if you want to read it all...).

Both speak TCP/IP, and RSX also speaks DECnet if you want to explore
other networking technologies.

They both come with compilers and tools. With Unix it's C (obviously),
and most of the standard tools you might expect.
RSX have C, Fortran, Basic, Pascal, Cobol, Lisp, Forth, and some others
if you start digging around. You also have some database like tools, and
so on.

The most obvious internet tools are available on both as well, such as
telnet, ftp and mail. RSX also have a web server and some other silly
things. You can probably find similar things for 2.11BSD as well if you
search around.

Other options for OSes are RSTS/E, which is a time sharing OS, and
RT-11, which is more of a single user realtime system.

There are others as well, but I think these are the more commonly used
options.

> Any "getting started" other than the official website?

I think I've come across several. Maybe just google for the different OSes?

Johnny

[Clem Cole]

On Tue, Jan 27, 2026 at 10:12 AM Robb Bates <robb...@gmail.com> wrote:

Hi all,

I just ordered my PiDP-11.  I doubt I'll have any issues with the build.

Pro tip: before you start HW assembly, go to https://obsolescence.wixsite.com/obsolescence/pidp-11-how-to-use and follow the instructions to download Oscar's PiDP-11 manual: https://obsolescence.dev/pidp11/PiDP-11_Manual.pdf.  That said, one small erratum in the Manual: on page 26, Oscar points you to Angelo's website, but the links http://a.papnet.eu/UNIX/v7/files/doc/ and http://a.papnet.eu/UNIX/v7/files/doc/03_beginners.pdf are dead.  However, you can find the documents at: http://squoze.net/UNIX/v7/files/doc/  and http://squoze.net/UNIX/v7/files/doc/03_beginners.pdf

Familiarize yourself with it, including how to and set up your target RPi (which will be fully functional before you add the 'blinkenlights.' ).  One hint, if you possibly can, run the RPi on real Ethernet, not WiFI.  It can work to some extent with WiFi in many cases, and on page 51 of Oscar's document, he offers hints.  But remember, the hosted operating systems, if they had network support back in the day, did not have WiFi, and assumptions were made about network support for the hosted OS.  The different PiDP-x mailing lists, as well as the SIMH list, have numerous threads by people, particularly new to the Unix family, who have run into trouble.  So using a hardware will eliminate some potential issues.

.  It is recommended that you set up the RPi as 'headless,' using SSH and VNC for connectivity.  In fact, getting that work done before you start the PiDP-11 SW download is advised.  There are numerous ways to make small errors. If you do everything incrementally, it will help you isolate the issues.

Also, if you plan to attach real serial ports via USB to the RPi, get the RPi talking properly to the terminals and working first, particularly if you are new to the RPi's flavor of Linux (Raspbian, which is similar to, but not 100% compatible with, Ubuntu).  If you do plan to set up serial ports on the PiDP-11 that the hosted OS uses, send me a note on the list.  I have a document on using serial ports that needs to be folded into Oscar's, but both he and I have been living PiDP-10 and PiDP-1, and we have not made that so.

When you have the RPi set up and are ready to install the applications and the different hosted OSs,  on the RPi, you can run these commands:

cd /opt
sudo git clone https://github.com/obsolescence/pidp11
/opt/pidp11/install/install.sh

Note that under the covers, the install script will perform: wget -O /opt/pidp11/systems.tar.gz http://pidp.net/pidp11/systems24.tar.gz

This will download the different hosted OS that simh will run (see below).

 It would also be helpful if you download the three SIMH manuals

• user guide: https://simh.trailing-edge.com/pdf/simh_doc.pdf 
• FAQ: https://simh.trailing-edge.com/pdf/simh_faq.pdf
• PDP-11: https://simh.trailing-edge.com/pdf/pdp1_doc.pdf

Note that those are the manuals for SIMH Version 3.  The version of SIMH that Oscar forked for the PiDP-11, which he added the "REALCONS" support for his display in the PDP-11 simulator, was an August 2019 4.0 [before 4.0 became private].  The FOSS-based OpenSIMH https://github.com/open-simh/simh is Version 4.1, but it lacks REALCONS support [details of why this is the case can be found in the historical archives of the simh mailing list - the short form is that OpenSIMH (https://opensimh.org/) plans to add REALCONS to all of their simulations, but to do that properly and be a general solution for all 40-odd simulators will take some surgery/refactoring.  For the new user, they are not important [email me offline and I'll take you through it].

I also understand there are several OSes built in.

Indeed: except for the Nankervis distribution, these are OSses you downloaded with wget.  [Nankervis is described in the PiDP-11 manual and is an option set of OS images; optionally, the install script will install a modified RSX11, which includes IP/TCP support, as well as version 2.11BSD with a number of patches applied since the original installation was created.]

It will save time if you understand how to run the hosted OS's under SIMH - so use the resources available, such as the bitsaver's PDF archive (see below).

 

 

I'm just wondering if there is a commonly used one and/or some resources or applications for them.

Ignoring idled and blinky, which are standalone programs to twiddle Oscar's display, the others come in two flavors: DEC Systems [DOS-11, RT11, RSTS/7, RSX1 - but not Ultrix11, which is available separately] and Unix-based [Research Unix Forth Sixth and Seventh editions, BSD 2.11, and formal AT&T releases (System III and V).

The core idea is that you use any of these systems to explore how they were used when they were released.  If you look in bitsavers, much of the DEC PDP-11 documentation can be found: http://www.bitsavers.org/pdf/dec/pdp11/  Similarly, if you look at "The Unix Heritage Society" (https://www.tuhs.org/), you can find the Unix source and much of the documentation [if you're serious about UNIX, join the TUHS mailing list described on their homepage].   

Also, it would not hurt to join the SIMH mailing list by visiting their home page https://groups.io/g/simh and pressing the "Join This Group" button.

The second chapter of Oscar's User Guide is "A Quick Tour through PDP-11 Operating Systems," which includes the last two research systems (V6, V7), BSD2.11, and two DEC operating systems (RSX11 and RT11).  As Oscar points out, V6 is the system that John Lions documented [http://www.lemis.com/grog/Documentation/Lions/ or buy it https://www.amazon.com/Lions-Commentary-Unix-John/dp/1573980137/ref=sr_1_1].  BTW: 

The Sixth edition of UNIX is still used today in OS courses at MIT, CMU, and a few other schools.  They use a version called xv6 (https://github.com/mit-pdos/xv6-public), which they describe as "a re-implementation of Dennis Ritchie's and Ken Thompson's Unix Version 6 (v6). xv6 loosely follows the structure and style of v6, but is implemented for a modern x86-based multiprocessor using ANSI C."

Seventh Edition is the classic UNIX, and what all modern UNIX reimplementations use as their core model. If you have never used a flavor of UNIX, Brian Kernighan's  "Unix for Beginners — Second Edition [http://squoze.net/UNIX/v7/files/doc/03_beginners.pdf] is a good place to start.  And if you want to be a better Unix or Linux user, one of the best ways to spend your time is to get a copy of "The UNIX Programming Environment" (a.k.a. UPE) and do all the exercises using V7, which the book was based [well, it was based on a V7+ system, from Research - there is only excersize that I know of that will fail on stock V7, due to the original Bourne Shell.  Bourne's work was first made available on V7 as the shell (replacing Ken's = which is what is in all earlier Unix implementations).  Originally, Bourne Shell did not support the hashmark (#) as a comment character.  That said, a replacement version of the binary is available from people like me in TUHS.

Oscar has a nice section on 2.11BSD.  He helps explain the networking setup that you will need to perform.  He also points to an excellent set of documents from Rene Richarz, with lots of how-tos, from programming in C and Pascal to building a networked weather station on 2.11BSD and using (simulated or real) Tektronix graphics terminals. 

Note that there is some background to help understand/explain how 2.11BSD was created.   Remember that V6, UCB released the 'Berkeley Software Distribution' (BSD — https://www.tuhs.org/cgi-bin/utree.pl?file=1BSD) for UNIX [if you look at the old USENIX tape on TUHS, you'll find a lot of institutions besides UCB released their own sets of additions and fixes].  Around the time V7 was released, the original BSD tape was updated to be 2BSD [https://www.tuhs.org/cgi-bin/utree.pl?file=2BSD].  Soon thereafter, the first Vax system, 3.0BSD [https://www.tuhs.org/cgi-bin/utree.pl?file=3BSD], was released, followed by 4.0 [https://www.tuhs.org/cgi-bin/utree.pl?file=4BSD] and 4.1BSD [https://www.tuhs.org/cgi-bin/utree.pl?file=BBN-Vax-TCP}. 4.1BSD was widely distributed and used around the world. 

An important feature of the BSD's starting with 3.0 was that the C compiler supported the IPL 32 programming model of the VAX, while a PDP-11 (IP16 L32 model).  This programming model allowed many programs and kernel features to be added.  But a group of dedicated people began bringing many of those programs and kernel features back to V7.  2.11BSD is the result of that work. 

2.11BSD should have a "user feel" that is similar to modern Unix systems, but the primary maintainer (Steven Shultz) is clear: he is not trying to make a complete copy of 4.2BSD on a PDP-11, so you will find differences and a lot of "missing" tools - the latter is a direct result of not enough address space, although thanks the overlay support that DEC donated to the Berkeley team (they had developed them in two of there Unix releases: V7m and Ultrix-11) if you are will work, it is possible to "back port" soome programs.

As for programming language support, the Research versions obviously all support C as their native language.  But with them are other language processors (many of them have multiple versions) from Basic, APL, snobol, Fortran-77, and Pascal. But remember that the dialects of these language processors may be different from what you might be used to.   One of the pieces of work with 2.11BSD is bringing a C89 (Ansi) version of C forward, as the Unix versions you will find on Oscar's tape are based on the C compiler (and language definition) at the time of release.

Again, in all cases, there will be a games directory already there.  But there are also many games available from various sources, including the TUHS site [https://www.tuhs.org/] and the bitsaver's DEC archives.

The two AT&T releases, System III and System V, are also available.  You will likely find that they are not as well-adorned as the Research and UCB versions. Certainly, compared to 2.11BSD.  But they are true to the time and might be interesting to compare them to both the Research and BSD releases.

As for DEC's OS, the first I'll point out is also Unix/V7 based - Ultrix-11, which you can download to your RPi from Bitsavers: http://www.bitsavers.org/bits/DEC/pdp11/magtapes/ultrix-11/#:~:text=Ultrix11%2Dinstall.tap.gz and information on how to install it from Gunkies: https://gunkies.org/wiki/Installing_ULTRIX-11_V1.0_on_SIMH  Note TUHS has the other DEC Unix release — v7m [https://www.tuhs.org/Archive/Distributions/DEC/Jean_Huens_v7m/], I'll not say much more than it is V7, plus some new peripherals and kernel has Fred Cantor's overlay code -- this is the system 2.11BSD is derived.

Ultrix-11 has C, Fortran, and PDP-11 assembler from DEC.  However, between the BSD 2 release, USENIX, and DECUS, multiple LISP and Pascal implementations ran quite well, and it is reported that both Algol and Basic-Plus-2 were available (but I never saw them or looked for them specifically).

The first two traditional "single user" DEC OS's that you will have installed are DOS-11 and RT11.  DOS-11 supports Macro-11, FORTRAN-IV, and BASIC.  RT-11 supports these, but also supports FORTRAN-77 and BASIC-11, with C and Pascal available from DECUS and other sources.  For instance, OMSI Pascal can be found on bitsavers at http://bitsavers.trailing-edge.com/bits/DEC/pdp11/discimages/rk05/omsiPascal2.1.dsk.gz

DEC then had two offerings that supported multi-user configurations:  RSTS and RSX11.  RSTS supported the same languages as RT-11, but also added BASIC-PLUS-2, PDP-11 COBOL, APL, and DATATRIEVE-11.  Looking in the DECUS archives and such, Pascal and C are available.  Similarly, RSX11 offers the same languages.   

BTW: If you have a PiDP-10, DEC offered a BLISS-11 crosscompiler that can target RT-11, RSTS, and RSX-11.

In all of these cases, if you look at https://bitsavers.org/bits/DEC/DECUS/PDP-11/ you will find directories for these three OSes.   There are all sorts of gems to be found, from games to serious programs.  Similarly, https://bitsavers.org/pdf/dec/pdp11/ has also sorts of documentation

Have fun.

 

[Tim Boan]

Clem,

Very nice writeup.

Tim Boan

Virus-free.www.avast.com

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[terri-...@glaver.org]

On Tuesday, January 27, 2026 at 9:58:21 PM UTC-5 cl...@ccc.com wrote:

 It is recommended that you set up the RPi as 'headless,' using SSH and VNC for connectivity.

This is not what the installation script considers "headless". That would still be a GUI install.
Headless is only when you install the Raspberry Pi OS from the "with no desktop environment"

distribution kit. Headless startup is a bit broken in both Oscar's repo and my fork (more on that

below) but will be fixed in the new installer (likewise, below).

Be careful if you want the X11 desktop instead of the default Wayland. You can't just do what

the Raspberry Pi documentation suggests and just use raspi-config / Advanced Options to

switch - you'll get a grey desktop that is completely unresponsive. You need to disable VNC

before you make the switch and re-enable it after. Also, if you use one and install the PiDP-11

software on the desktop and then switch, it won't be on the new desktop. Just re-run the install.
This is a Raspberry Pi OS defect and not anything specific to the PiDP-11.

[...]particularly if you are new to the RPi's flavor of Linux (Raspbian, which is similar to, but not 100% compatible with, Ubuntu).

It hasn't been called Raspbian in quite some time. It's now just "Raspberry Pi OS" which is

based directly on Debian, but with a large number of "creature comforts" preinstalled.

IMPORTANT: You should download and use the "Bookworm" release. "Trixie" is mostly un-

tested with the PiDP-11 at this time.

Also, the terminal emulators are mostly broken (most investigation and fixes deferred to

a future release). Just use the standard terminal you get by clicking on the terminal icon

on the menu bar.

 

Also, if you plan to attach real serial ports via USB to the RPi, get the RPi talking properly to the terminals and working first

I strongly disagree with this part. Enabling Raspberry Pi OS (Linux) logins on the terminals

will greatly complicate your later PDP-11 OS setup. Just connect the hardware and you

should see a /dev/ttyUSBn appear for each serial port. That's the only thing you need to do

at the Raspberry Pi OS level.

Then (advanced) modify the appropriate boot.ini in /opt/pidp11/systems to add something

like this:

;
; Set up the USB-to-serial ports on the RPi
set vh lines=16
set vh dhu
set vh nomodem
set vh enable
;
; Note that these are "shuffled" so the cabling matches the panel
attach vh line=0,connect=/dev/ttyUSB0
attach vh line=1,connect=/dev/ttyUSB1
attach vh line=2,connect=/dev/ttyUSB3
attach vh line=3,connect=/dev/ttyUSB2

Note that only the newer PDP-11 operating systems support the vh/dhu interface. For the

others, you should use dz.

This is somewhat documented in Oscar's web site under "Hacks / Adding 4 serial ports": 

https://obsolescence.dev/pidp-11-connectivity-options.html

but much useful information was lost when he redesigned his web site - including the

actual steps as shown above. [The 2nd picture in that section showing the USB/serial

adapters was provided by me as I was the first to do it, way back in 2018. A better pic-

ture (newer, with Raspberry Pi 5 and NVMe adapter) is attached.

 When you have the RPi set up and are ready to install the applications and the different hosted OSs,  on the RPi, you can run these commands:

cd /opt
sudo git clone https://github.com/obsolescence/pidp11
/opt/pidp11/install/install.sh

I'd just point out that the bugfix+feature fork is at: https://github.com/Terri-Kennedy/pidp11

This is an officially sanctioned (by Oscar) fork which will (when finished) merge back to the

main obsolescence branch.

A few notes: you must select compile rather than pre-installed binaries as they have not been

updated (I'm working on a new installation script with many changes, and haven't been pushing

commits to the branch). If you have "backwards" knob rotation or want to have different startup

settings for the Address and Data knobs, you need to copy /opt/pidp11/install/pidp11-useroptions.rc

to /opt/pidp11 and edit it (it's a text file) appropriately. The [eventual] new installer will clean all of

this up, as well as adding many other goodies.