Running VAX Ultrix 4.5 on simh

Not a long entry here, since all the hard work was already done by Darkstar @

I only wanted to add my additions (tun-tap networking and remote X11 DECwindows via Xephyr)

The main difference is the ultrix.ini configuration file, since we will be using tap0 and bridging and setting up masquerade on our Linux machine, below is my script that I run before the simh simulator starts

#Setup tap and bridge 
tunctl -t tap0 -u user
ifconfig tap0 up
brctl addbr br0
brctl setfd br0 0
ifconfig br0 netmask broadcast up
#brctl addif br0 tap0 vboxnet0 <-- add this if you wish to integrate with VirtualBox
brctl addif br0 tap0 
ifconfig tap0
sysctl net.ipv4.ip_forward=1
iptables --table nat -A POSTROUTING --out-interface wlan0 -j MASQUERADE

Next is the ultrix.ini simh configuration file that I have used

; SimH 4.0 Configuration file for MicroVAX 3800
; Host System : DEC MicroVAX 3800
; Operating System : DEC Ultrix v4.5
; Memory : 64mb
; Network config : XQ: Ethernet, 08:00:2b:04:14:02
; Disks : RQ0: RA90, 1.2gb
; RQ1: RA90, 1.2gb
; CDROMs : RQ2: iso file
; Tape config : TQ0: TK50, 94mb

load -r ka655x.bin

attach NVR nvram.bin

; CPU config
set CPU 64m
set CPU conhalt
set CPU idle=all

; configure console to 7-bit only
set TTO 7b
set TTI 7b

; Disk drives
set RQ0 ra90
attach RQ0 disk01.dd 
set RQ1 ra90
attach RQ1 disk02.dd 
attach -r RQ2 ultrix.iso
set RQ3 dis

; Tape
set TQ tk50
;attach tq0 filename-to-tape-file
set TQ1 dis
set TQ2 dis
set TQ3 dis

; Disable unused peripherals
set CR dis
set RL dis
set TS dis

; Attach Ethernet to a network interface
set xq mac=08-00-2B-AA-BB-CC
attach xq tap:tap0

; boot the system
boot CPU


The ka620.bin is from here

The ultrix.iso is from here  Just bunzip2 and rename to ultrix.iso

The disk01.dd and disk02.dd are made like this

dd if=/dev/zero of=disk01.dd bs=1024 count=1M
dd if=/dev/zero of=disk02.dd bs=1024 count=1M


So one can pretty much follow 100% the steps in the except in the following section where I have chosen DECwindows for OSF/Motif (1)

I have used slightly different network config because of the tap setup earlier so we will change this section accordingly

I have used these values

# ifconfig qe0 netmask up
# route add default 1

Once we reboot and have everything working (network) we move on to configuring the DECwindows part. For this I have changed the following file in order to load DECwindows motif  /usr/lib/X11/xdm/Xsession


exec > $HOME/.xsession-errors 2>&1

case $# in
case $1 in
exec xterm -geometry 80x24-0-0


if [ -f $startup ]; then
exec $startup
if [ -f $resources ]; then
xrdb -load $resources
exec /usr/bin/dxsession 

Then I have created a symlink to xdm so I could call startx from root directly

# ln -s /usr/bin/X11/xdm /startx

Then if I wanted to run DECwindows just initiate startx

# ./startx

And on my Linux host I run Xephyr as follows

Xephyr -screen 980x640 -ac -query :3

Which gives me a nice remote DECwindows environment to work with

There are some interesting VAX Ultrix resources still available online today like GCC 3.0.4 is there if you don’t like the DEC C compiler.

Stephen's Machine Room -



About astr0baby

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6 Responses to Running VAX Ultrix 4.5 on simh

  1. Another option is to run Ultrix 4.5 on MIPS in GXEmul:
    I had it running about 10 years ago.
    Also GXemul supports (although not listed in the site) DEC OSF 1 on MIPS (I can confirm v1 works, v2 never tried/didnt have at the time):

  2. And another thing which is a bit offtopic but still DEC related is that VMSSoftware now have OpenVMS running on x86_64 (so far in a VM only):
    They confirmed there will be a Hobbyist program for OpenVMS (but not the VAX version). I was thinking it may be of interest to you and perhaps about v9.1 you may ping them to get access to it even if the hobby program is not active yet. I have two Alphas and I was a participant of HPs Hobbyist program 10 years ago and Im looking forward to the x86 port since I cant get access to an Itanium. (I should have pinged you on Twitter but I just dont use it)

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