Initial commit of 2.11BSD disk image and instructions.
[pdp11-211bsd-simh] /


The 211bsd_simh directory contains a working 2.11BSD disk image that can be booted using the included SIMH config file. Simply execute simh system.conf from within the 211bsd_simh directory. Don’t forget to gunzip the disk image file before use.

If you need help installing/configuring SIMH, see my notes on installing SIMH located at

If your console looks like the contents of the files in 7bit-encoding, make sure the line set tto 7b is not commented out in 211bsd_simh/system.conf.

The files in 211bsd_install_tape are a BSD install tape image and a PDF describing how to use it.


Tested and working. This image runs regularly in SIMH and a real PDP-11.


Clone the repository and un-gzip the disk image.

git clone git://
cd pdp11-211bsd-simh/211bsd_simh
gunzip disk0_ra90_211bsd.dsk.gz

From within the same directory, execute pdp11 system.conf to begin the simulation using SIMH.

PDP-11 simulator V3.9-0
Disabling CR
Disabling RK
Disabling HK
Disabling TM

73Boot from ra(0,0,0) at 0172150

This bootloader was loaded from block 0 of the first MSCP compatible disc device, which, per system.conf, is the file disk0_ra90_211bsd.dsk. This bootloader is sophisticated enough to load the UNIX kernel, but we have to tell it what device and file to load. Type ra(0,0,0)unix and press Enter to proceed.

: ra(0,0,0)unix
Boot: bootdev=02400 bootcsr=0172150

2.11 BSD UNIX #1: Sat Aug 11 20:38:20 PDT 2018

    ra0: Ver 3 mod 3
    ra0: RA90  size=2376153

    phys mem  = 4186112
    avail mem = 3990464
    user mem  = 307200

    August 12 00:01:47 init: configure system

    ra 0 csr 172150 vector 154 vectorset attached
    cn 1 csr 176500 vector 300 skipped:  No CSR.
    cn 2 csr 176510 vector 310 skipped:  No CSR.
    cn 3 csr 176520 vector 320 skipped:  No CSR.
    cn 4 csr 176530 vector 330 skipped:  No CSR.
    erase, kill ^U, intr ^C

The computer has now booted up to single-user mode and you are logged in as root. Unless you need to perform an operation in single-user mode, press Ctrl-D here to logout and let startup continue.

    # Fast boot ... skipping disk checks
    checking quotas: done.
    Assuming non-networking system ...
    checking for core dump...
    preserving editor files
    clearing /tmp
    standard daemons: update cron accounting.
    starting lpd
    starting local daemons: sendmail.
    Sun Aug 12 00:01:53 PDT 2018

    2.11 BSD UNIX ( (console)


2.11BSD is now booted into multi-user mode. Login with username root and password temppass to get started.

To shut down, as root, type sync; sync; halt to flush any buffers and halt the PDP-11 simulation. Then, type quit at the sim> prompt to exit SIMH.

    login: root
    erase, kill ^U, intr ^C
    # sync; sync; halt
    syncing disks... done

    HALT instruction, PC: 000014 (MOV #1,10544)
    sim> quit

Note that you can always halt the simulation and return control to SIMH by pressing Ctrl-e at any time. This drops to the sim> prompt. Entering go will resume simulation where it paused.