[TUHS] Bootstrapping UNIX - how was it done

[James Frew via TUHS]

Our (v6++) 11/45 wasn't especially flakey, but it did have a primitive 
frame buffer attached to it that I was debugging a driver for, so I 
wound up getting up close and personal with the rebooting process, to 
the extent that I had actually memorized the multiple instruction 
sequence (now, thankfully, forgotten) that had to be keyed in to restart 
it. Have to say I was both proud and horrified to be *programming a 
computer with switches*...

/Frew

On 2026-03-23 3:11 AM, John P. Linderman via TUHS 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