Overview

This directory contains a V5 UNIX system image for use with the PDP-11 simulator included in SIMH. The image was taken from a PDP-11/45 with an RK05 disk (2.4 MB).

V5 UNIX was the first version licensed widely outside AT&T, largely due to Thompson and Ritchie’s CACM paper that had recently introduced UNIX to the world.

Version 5 still only targeted PDP-11s, but expanded to include those models with an 18-bit physical address space, compared to the 16-bit address space of previous models. This allowed up to 256 kB of RAM and greatly increased the capabilities of the system, needed as UNIX reached “above 50” installations at the time of this release.

This is the second release of UNIX written in C, a language still in flux that had only existed for a couple years. The system is self-hosting using the included compiler but there are many differences from modern C visible in the on-disk source code.

Old enough to predate the Bourne shell from Steve Bourne, V5 UNIX ships with the Thompson shell written by Ken Thompson. This was the first UNIX shell, mainly a command interpreter rather than the interpreted language that most UNIX shells became. Intentionally minimal, commands like if and goto are implemented as separate executables rather than as built-in shell commands. This shell was replaced by the Bourne shell in V7 UNIX and by the C shell in 2BSD, leading to its rapid decline in popularity.

Several now common commands were first introduced in this release, including dd, pwd, and wump (Hunt the Wumpus). At this stage it’s starting to feel like a UNIX system, though we must remember that cd is still chdir.

Then there’s the editor, ed. A UNIX classic, it’s a little like using vi with your eyes shut. If you’ve never used it before, check out my guide to ed.

Status

Fully tested on SIMH 3.9-0.

Instructions

Power On

To power up a simulated PDP-11/45 and run this V5 UNIX disk image, simply un-gzip the disk image file and start up SIMH with the provided configuration file.

% gunzip unix_v5_rk.dsk.gz
% pdp11 simh.conf

PDP-11 simulator V3.9-0
Disabling XQ
.
.Type kernel filename at the '@' prompt.
.For example: @unix.
.UNIX username is 'root'.
.No password.
.
@ 

The @ prompt is from the bootloader, to whom we must pass a file to continue the boot process. Our kernel is a file named unix, so type that here followed by ENTER.

@unix

;login:

The system has now booted up and you may login as root (no password).

;login: root
#

That’s it! V5 UNIX is up and you’re logged in.

Power Off

To power off, assuming you are logged in as root and the system is otherwise inactive, use the sync command to flush any buffers to disk and then type Ctrl-e to halt the simulation and quit to exit SIMH.

# sync; sync
# <Ctrl-e>
Simulation stopped, PC: 001726 (MOV (SP)+,177776)
sim> quit
Goodbye

Note that you can also press Ctrl-e at any time and SIMH will halt the PDP-11 simulation and drop to the sim> prompt where you can exit. However, doing this is likely to corrupt a disk as it is equivalent to yanking the power cord from the wall. To resume from the sim> prompt, simply type go and execution will resume from where it left off.

Transfer Files

One may output via the line printer, or input/output via the paper tape. The relevant options to enable that hardware in SIMH are commented out in simh.conf.

When offline, it is possible to mount the disk image and interact with it directly. For example, use https://git.subgeniuskitty.com/pdp11-unix-fusefs/.git.