[TUHS] Bootstrapping UNIX - how was it done

[ron minnich via TUHS]

I've still got my diode ROM from what was either an 11/45 or an 11/70. I've
given away my 11/45 and 11/70 front panels, sadly. By the time I came on
scene, in 1975 or so, to boot from (say) an RK05, you would flip the halt
swtich (usually a good idea), toggle in an address that was owned by the
diode rom, 177400, whatever, flip a momentary switch UP, not DOWN, to load
that starting address, release halt, and hit the momentary start switch. I
believe if you left HALT set, you could step it through the diode rom, but
that's an only memory.

But on the -8, we were toggling in code, and on the -11, we were toggling
in a starting address in a boot diode ROM -- much easier.



On Mon, Mar 23, 2026 at 10:20 AM John Levine via TUHS <tuhs at tuhs.org> wrote:

> It appears that Peter Weinberger (温�  � �) via TUHS <pjw at google.com> said:
> >As I remember, the 11/70 was booted just as John describes. One keyed
> >in a boot loader at the console.
>
> I'm pretty sure our PDP-11 at Yale had a boot ROM, so you just set
> the starting address from the switches and started it.
>
> Before that I toggled boot loaders into PDP-8's and I don't miss it.
>
> R's,
> John
>
>
> >
> >On Mon, Mar 23, 2026 at 3:11 AM John P. Linderman via TUHS
> ><tuhs at tuhs.org> wrote:
> >>
> >> >
> >> > >How was UNIX bootstrapped in the early days?
> >> >
> >> > When I started at the Labs in 1973, what eventually morphed into the
> >> Programmer's Workbench UNIX ran a PDP45 in Piscataway, NJ. UNIX was
> >> sufficiently flakey at that time that they liked to reboot the system
> each
> >> day to clean up corruption in the file system. Someone noticed that I
> >> arrived before 6 am every morning, when a reboot would go unnoticed by
> most
> >> people. So I was taught how to halt the system, set a bunch of keys on
> the
> >> front of the 45, and hit start. I'm guessing that the keys simply
> directed
> >> the 45 to read a boot block from some device, and execute the
> instructions
> >> in that block, where the real software bootstrapping began. I'm sure
> others
> >> in this group can supply the correct details. I was not then, and still
> am
> >> not now, a hardware person, but I remain an early riser. -- jpl
> >
>
>
>