So this is pretty neat. From the code we can see that:
If you set the console switches of the PDP-11 to the magic number 173030 init executes "/bin/sh -" on the console tty (probably a decwriter).
Otherwise it starts /etc/getty on /dev/tty0 - tty8, ttya, and ttyb.
It also starts /etc/dpd ("Dpd is the 201 data phone daemon. It is designed to submit jobs to the Honeywell 6070 computer via the GRTS interface."), /usr/mel/da (???) and /usr/demo/dds (???).
When user logs out it's copying the utmp entry to wtmp.
I can see that the init binary is 456 bytes.
It's mounting hard drives /dev/rk1-rk3 on /usr, /sys and /crp. Maybe no /etc/fstab yet. I guess /dev/rk0 had root.
It's not that magic. It's the address of the (RF disc) IPL in the "UNIX ROM". It allows the operator to bootstrap Warm UNIX into single-user mode by just pressing LOAD then START without adjusting the front panel switches. Bootstrapping Warm UNIX into multi-user mode is achieved by just toggling one front panel switch (#15) in between LOAD and START. It's all described in the accompanying boot(7) manual page.
I would look in the git repository for Unix: https://github.com/dspinellis/unix-history-repo. It isn't guaranteed to be correct, either, but should have a commit describing its addition that can be trusted slightly more.
If you set the console switches of the PDP-11 to the magic number 173030 init executes "/bin/sh -" on the console tty (probably a decwriter).
Otherwise it starts /etc/getty on /dev/tty0 - tty8, ttya, and ttyb.
It also starts /etc/dpd ("Dpd is the 201 data phone daemon. It is designed to submit jobs to the Honeywell 6070 computer via the GRTS interface."), /usr/mel/da (???) and /usr/demo/dds (???).
When user logs out it's copying the utmp entry to wtmp.
I can see that the init binary is 456 bytes.
It's mounting hard drives /dev/rk1-rk3 on /usr, /sys and /crp. Maybe no /etc/fstab yet. I guess /dev/rk0 had root.