2.11BSD on an MSCP disk, on the LAN

Verified on real hardware

QUniLator 1.16.0-1, 2026-08-06, on a real KDJ11-D (PDP-11/53) in a QBUS backplane. The processor is real; QUniLator supplies the disk and the Ethernet.

What you will have at the end

A PDP-11 running 2.11BSD multi-user, with a UNIX filesystem on a disk that is a file and an Ethernet address on your own network — reachable by telnet from your desk.

If XXDP proved the machine works, this is the one that makes it useful.

The machine

Processor	Real KDJ11-D (PDP-11/53) — 1.5 MB of its own memory, its own boot ROM and console line
Backplane	QBUS, QBone in a quad slot
From QUniLator	A UDA50 MSCP controller with one RA81, and a DELQA Ethernet controller

Three devices. The processor supplies everything else.

What you need

• A 2.11BSD MSCP disk image. The one here is du/2.11BSD_qbone.dsk, a 1 GB volume carrying a kernel built for this machine.
• A free address on your LAN, and its gateway. This walkthrough uses 192.168.2.180 with gateway 192.168.2.1 — substitute your own.
• The console line cabled and its speed set, per the XXDP walkthrough.

1. Build the machine

On Configurations, start from default (everything off) and add three devices:

Device	Setting
uda	the UDA50 controller, defaults are right
uda0	an RA81 holding du/2.11BSD_qbone.dsk
delqa	the Ethernet controller, on interface veth-pdp

Leave DL11 disabled — the processor has its own console.

Set the image before you enable the drive

Enabling the controller rebuilds the drives under it, which clears an image assigned beforehand. Assign the image, then enable — and check the drive reports READY with a non-zero capacity before going on.

The disk announces itself by the image’s size rather than the drive type’s, which is what lets a 1 GB volume live on a drive DEC built at 456 MB. You will see it in the boot log.

2. Switch it on and boot

Press AUX ON/OFF. The processor’s ROM counts down and finds the MSCP disk:

9 8 7 6 5 4 3 2 1

DU0
53Boot from ra(0,0,0) at 0172150
:

The : is 2.11BSD’s boot block asking which kernel to load. Answer:

ra(0,0,0)unix

Type it one character at a time

The serial line has no receive buffer worth the name. Pasting ra(0,0,0)unix as a burst arrives as r,)x and the boot fails. The browser console types at human speed and is fine; a script must pace each character on its echo.

The kernel comes up and tells you what it found:

UNIX #1: Sep 10 12:20:06 PDT 2019
    root@Tue:/usr/src/sys/QBONE

ra0: Ver 3 mod 6
ra0: RA81  size=1953301
attaching qe0 csr 174440
qe0: DEC DELQA addr 08:00:2b:55:a3:67
attaching lo0

phys mem  = 1572864
avail mem = 1174912

Three lines worth reading. size=1953301 is the image’s block count, not an RA81’s. qe0 is the DELQA, and its address is derived from the BeagleBone’s own MAC, so it is unique without you choosing one. phys mem = 1572864 is the processor’s own 1.5 MB — QUniLator supplied none of it.

You land in a single-user shell at #.

3. Point it at your network

2.11BSD reads its network settings from /etc/netstart and resolves its own name through /etc/hosts. A stock image is set up for whatever LAN it was built on, so both need repointing — after which every reboot comes up on the network by itself.

sed -e 's/^broadcast=.*/broadcast=192.168.2.255/' \
    -e 's/^default=.*/default=192.168.2.1/' /etc/netstart > /tmp/ns
cp /tmp/ns /etc/netstart

sed 's/^10\.0\.1\.212/192.168.2.180/' /etc/hosts > /tmp/h
cp /tmp/h /etc/hosts

The second one matters and is easy to miss: netstart passes the hostname to ifconfig, so the address the machine gets is whatever /etc/hosts maps that name to.

netmask is already 255.255.255.0. Leave routedflags=NO alone — the file says why, in capitals.

4. Go multi-user

Press Ctrl-D. netstart runs, and the daemons come up:

Assuming NETWORKING system ...
add net default: gateway 192.168.2.1
starting system logger
starting network daemons: inetd rwhod printer.
starting local daemons: sendmail ntpd.

2.11 BSD UNIX (pdp11) (console)

login:

5. Reach it from your desk

$ ping -c3 192.168.2.180
3 packets transmitted, 3 packets received, 0.0% packet loss

$ telnet 192.168.2.180

2.11 BSD UNIX (pdp11)

login:

That login prompt came off a PDP-11, over an Ethernet controller that is software, out of a disk that is a file.

What can go wrong

The boot block says : and nothing you type works	Characters are being dropped. Type slower, one at a time.
The drive shows capacity 0	The image was assigned before the controller was enabled and got cleared. Assign it again.
Hard errors, then a corrupted filesystem	The volume is bigger than the drive type and is being truncated. Check the boot log says size= the image’s block count.
Multi-user hangs with the console dead	A serial mux fighting for interrupt time. Disable dzv11 if you have it enabled; this machine does not.
ping is not found in single-user	/usr is not mounted yet. Go multi-user first.
Nothing on the LAN	Check the DELQA’s interface parameter names the bridged interface (veth-pdp here). The host’s own address is not reachable from a raw socket on the same NIC — the bridge exists for that.

Next

Save As… the configuration — this one is saved as 211bsd — and bind it to a Power-on DIP setting so the machine boots into UNIX whenever it is switched on.

Then try the other direction entirely: VMS on an emulated VAX, where QUniLator supplies the processor too.