View Full Version : Graceful shutdown procedure on PDP-11?

March 20th, 2009, 07:42 AM

I have my PDP-11/53 build up to the point of installing RT-11.

One quesiton: is there a graceful shutdown procedure for this system? It just seems wrong to hit the 'off' switch like it's a DOS box.


Lou - N2MIY
March 20th, 2009, 03:16 PM

I'm not sure if it does any good, but I always halt the machine before turning it off. The reason I'm not sure it does anything is because the machine is still running - that is, when I press halt, it drops to ODT. At least I can be sure that it won't be doing any disk I/O.

Hopefully someone else has a suggestion.


March 20th, 2009, 03:49 PM
It depends on the OS. AFAIK RT-11 doesn't need any special shutdown sequence but I always issue a "sync" when I'm done in Unix.

I'm probably over-cautious, but I have a bit of a ritual with my PDP-11s. My power-up sequence is:

Switch off all the circuit breakers on attached drives
Start the CPU on halt (in my case, I have everything hooked up to the power controller(s), so this also routes power to the drives)
Switch on the drives one at a time
Insert disk packs if necessary, and spin the drives up
Take the CPU off of halt and hit reset

For powering down, it's pretty much the reverse:

Issue any OS-specific shutdown commands
Halt CPU
Spin down drives and remove disk packs
Turn off drives' circuit breakers
Turn off CPU

And probably some other steps I've forgotten about ;-) Basically I do as much as I can to be as easy on the hardware as possible.

March 20th, 2009, 06:35 PM
All this talk about power-up and power-down sequences is making me start to want a PDP.

March 21st, 2009, 03:36 AM
Lou, Cosam,

Thanks - halting the CPU and sequencing the disks makes a lot of sense. That's likely what modern OS's are doing with software-controlled hardware.


March 21st, 2009, 04:25 PM
All this talk about power-up and power-down sequences is making me start to want a PDP.
Oh yes, every serious collector should have at least one refrigerator-sized machine, preferably requiring 3-phase power ;-) Kidding aside though, some of the later Qbus machines aren't any bigger than a moderately large PC tower and still great fun to tinker with.

March 22nd, 2009, 04:21 AM
Cosasm is right, my PDP-11/53 will be housed in a 4U server case when I'm finished, but it could fit in a desktop case also. The Micro-PDP line were all in oversized tower cases...