RSX is a good operating system for process control systems as it is normally very stable. I have a system running on Simh under Ubuntu (also a stable operating system) that has been running for 224 days. In my work with real PDP-11 systems we only rebooted if we needed to update the operating system. This was possible since power failures did not cause reboots and this was before UPS was common. Later PDP-11s (e.g. 11/44) did not have core memory, but did have batteries to keep the semiconductor memory alive during power failures.

Still RSX is fairly tolerate of power failures and improper shutdowns. Normally the only error you might see is the system accounting file [1,6]ACNTRN.SYS might not be properly closed which can be fixed with a


At this point we can shutdown RSX as we've created the new disk with the increased file headers and the correct way to do this is shown below. Notice it dismounts all the disks and shutdown everything properly, including putting the control rods back in the nuclear reactor if necessary.


RSX-11M-PLUS Shut down program

Enter minutes to wait before shutdown: 0
Reason for shutdown (<CR> for none):
OK to shutdown? [Y/N]: Y
All further logins are disabled

1-JAN-14 16:35   System is now shutting down -- RSXMPL

16:35:49 SYSLOG -- 47. Exiting
>@ <EOF>
ACS -- Checkpoint file now inactive
DMO -- System disk being dismounted
DMO -- SYSTEM dismounted from DU0:   *** Final dismount initiated ***
16:35:51 *** DU0: -- Dismount complete
DMO -- SYSTEM dismounted from DU2:   *** Final dismount initiated ***
16:35:56 *** DU2: -- Dismount complete
SHUTUP operation complete

HALT instruction, PC: 126130 (CLRB @#177776)


At this point we no longer need the two disk images that were not changed.

#: rm rsx11mplus_4_6_bl87.dsk
#: rm rsx11mpbl.dsk
#: mv rsx11mpbl_mxf.dsk rsx11mp.dsk

We also can shorten the new bootable disk name and alter sim.ini to make the new disk the rq0 disk. It might not hurt to also make a copy of this disk in case you want to make additional RSX systems in the future.