Updated README for V5 UNIX.

[simh-images] / pdp11-V5_UNIX / README.md

# 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](https://www.bell-labs.com/usr/dmr/www/cacm.html) 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](https://subgeniuskitty.com/development/pdp-11/guide-to-ed-text-editor).


# 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>.